feat(computes): the host overview shows its VMs, capacity and load, also when it cannot be reached

A host the panel could not reach made its overview the 500 page,
without the host's sections, and the Computes list gave such a host an
Overview button that led nowhere. The page now keeps the host's name,
sections, "Edit connection" and "Remove from panel" (the existing
confirmation), and says "Not connected" with the reason and a "Try
again". Details that cannot be read are said in an alert; the VMs,
capacity and load still show, as they are read on their own.

A reachable host's page leads with what it runs and what it gave:
- its VMs by state (running, shut off, paused, other), linked to
  Instances;
- the vCPUs, memory and storage pools given, as on the Computes list,
  which now shares those parts (computes/capacity_*.html) and their
  preparation (views.shown_capacity) with it;
- CPU and memory in use, side by side, with the current reading in
  words, a note on what the charts hold and when they were last
  updated, or since when not; memory in GB like the rest of the page;
- Hardware and Software and connection: logical CPUs and clock from
  virNodeGetInfo, but physical cores, sockets and NUMA nodes counted
  from the CPUs of the capabilities' NUMA cells, as virNodeGetInfo
  makes a topology up for hosts it cannot describe (asymmetric NUMA);
  the hypervisor's own name and version, libvirt, emulator, the guest
  architectures as text instead of menus of dead links. A host without
  sysinfo shows no processor instead of failing.
Empty notes no longer show "None"; labels stack over their values on a
phone instead of running into them.

Pools that cannot be read no longer drop a host's vCPUs and memory from
its capacity: the storage part says so. get_capacity also counts the
VMs by state.

computes/views.py

@@ -30,28 +30,36 @@ CPU_SAMPLE_MAX_AGE = 15
 CPU_SAMPLE_SIGNER = signing.TimestampSigner(salt="computes.cpu-sample")
 
 
+def shown_capacity(compute):
+    """The compute's capacity, with what its bars show; None when it cannot
+    be read."""
+    given = compute.capacity
+    if given:
+        # the memory bar: running and shut-off VMs' memory, and a mark at the
+        # host's memory, on a scale that holds whichever is larger
+        assigned, memory = given["assigned"], given["memory"]
+        scale = max(assigned["all"], memory) or 1
+        given["bar"] = {"running": assigned["running"] * 100 / scale,
+                        "stopped": (assigned["all"] - assigned["running"]) * 100 / scale,
+                        "host": memory * 100 / scale, "over": assigned["all"] > memory}
+        given["memory_percent"] = round(assigned["all"] * 100 / memory) if memory else 0
+        given["vm_count"] = sum(given["vms"].values())
+        # the default pool (else the first) shows; the others (a host may
+        # have dozens) open on a click
+        pools = given["pools"] or []
+        for pool in pools:
+            pool["used_percent"] = (pool["size"] - pool["free"]) * 100 / pool["size"] if pool["size"] else 0
+        given["pool"] = pools[0] if pools else None
+        given["more_pools"] = pools[1:]
+    return given
+
+
 @superuser_only
 def computes(request):
     """The computes, with what each has given its VMs."""
     computes = list(Compute.objects.order_by("name"))
     for compute in computes:
-        given = compute.capacity
-        if given:
-            # the memory bar: running and shut-off VMs' memory, and a mark at the
-            # host's memory, on a scale that holds whichever is larger
-            assigned, memory = given["assigned"], given["memory"]
-            scale = max(assigned["all"], memory) or 1
-            given["bar"] = {"running": assigned["running"] * 100 / scale,
-                            "stopped": (assigned["all"] - assigned["running"]) * 100 / scale,
-                            "host": memory * 100 / scale, "over": assigned["all"] > memory}
-            given["memory_percent"] = round(assigned["all"] * 100 / memory) if memory else 0
-            for pool in given["pools"]:
-                pool["used_percent"] = (pool["size"] - pool["free"]) * 100 / pool["size"] if pool["size"] else 0
-            # the default pool (else the first) shows; the others (a host may
-            # have dozens) open on a click
-            pools = given["pools"]
-            given["pool"] = pools[0] if pools else None
-            given["more_pools"] = pools[1:]
+        compute.shown_capacity = shown_capacity(compute)
     return render(request, "computes/list.html", {"computes": computes})
 
 
@@ -65,33 +73,29 @@ def capacity(request, compute_id):
 
 @superuser_only
 def overview(request, compute_id):
+    """The host's page: whether the panel reaches it, its VMs, what it has
+    given them, its load, hardware and software. A host it cannot reach
+    keeps the page, with the reason and its connection to edit."""
     compute = get_object_or_404(Compute, pk=compute_id)
     # the connection itself, not a TCP probe: ssh aliases and ProxyJump hosts
     # are not reachable by name and port from here
-    status = "true" if compute.status else "false"
-
-    conn = wvmHostDetails(
-        compute.hostname,
-        compute.login,
-        compute.password,
-        compute.type,
-    )
-    (
-        hostname,
-        host_arch,
-        host_memory,
-        logical_cpu,
-        model_cpu,
-        uri_conn,
-    ) = conn.get_node_info()
-    hypervisor = conn.get_hypervisors_domain_types()
-    mem_usage = conn.get_memory_usage()
-    emulator = conn.get_emulator(host_arch)
-    version = conn.get_version()
-    lib_version = conn.get_lib_version()
-    conn.close()
-
-    return render(request, "overview.html", locals())
+    context = {"compute": compute, "connected": compute.status is True}
+    if context["connected"]:
+        try:
+            conn = wvmHostDetails(compute.hostname, compute.login, compute.password, compute.type)
+            hostname, arch, memory, _cpus, processor, uri = conn.get_node_info()
+            context["host"] = {
+                "hostname": hostname, "arch": arch, "memory": memory, "processor": processor, "uri": uri,
+                "topology": conn.get_cpu_topology(),
+                "hypervisor": conn.wvm.getType(), "hypervisor_version": conn.get_version(),
+                "libvirt_version": conn.get_lib_version(),
+                "emulator": conn.get_emulator(arch), "guest_archs": conn.get_hypervisors_domain_types(),
+            }
+            conn.close()
+        except libvirtError as error:
+            context["read_error"] = str(error)
+        context["given"] = shown_capacity(compute)
+    return render(request, "overview.html", context)
 
 
 @superuser_only