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/models.py

@@ -91,18 +91,22 @@ class Compute(Model):
     @cached_property
     def capacity(self):
         """What the host has given its VMs (wvmHostDetails.get_capacity), its
-        vCPUs per CPU, and its active storage pools, the default one first; or
-        None when it cannot be read."""
+        vCPUs per CPU, and its active storage pools, the default one first
+        (None when the pools cannot be read); or None when the host cannot be
+        read."""
         if self.status is not True:
             return None
         try:
             given = self.proxy.get_capacity()
-            storages = wvmStorages(self.hostname, self.login, self.password, self.type)
-            pools = [pool for pool in storages.get_storages_info() if pool["status"]]
         except libvirtError:
             return None
         given["ratio"] = given["vcpus"]["all"] / given["cpus"] if given["cpus"] else 0
-        given["pools"] = sorted(pools, key=lambda pool: (pool["name"] != "default", pool["name"]))
+        try:
+            storages = wvmStorages(self.hostname, self.login, self.password, self.type)
+            pools = [pool for pool in storages.get_storages_info() if pool["status"]]
+            given["pools"] = sorted(pools, key=lambda pool: (pool["name"] != "default", pool["name"]))
+        except libvirtError:
+            given["pools"] = None
         return given
 
     def __str__(self):