fix(storages): pools are measured when shown, and only on a host's own pages

libvirt measures a pool's size and free space only when the pool is
refreshed and keeps those figures until the next refresh. The pool
lists read them without a refresh, so they showed a pool's space as of
whenever libvirt last refreshed it: two hosts sharing one pool's
storage told different free space for it, each its own refresh's. On a
test host, a 1 GiB file left libvirt's free space unchanged while df
showed 1 GiB less, until the pool was refreshed.

get_storages_info refreshes each active pool before reading it; a
refresh libvirt refuses (while a volume is cloned in the pool) leaves
the last figures, as the pool pages already do. A refresh scans the
pool's volumes, so pools are read only where one host's are shown: a
host's overview (views.host_pools, its Storage card) and its Storages
page and API. The Computes list and the new-VM dialog's host lines,
which read every host at once, no longer show pools; Compute.capacity
is the vCPUs and memory given.

computes/tests/test_cpu_graph.py

@@ -139,7 +139,7 @@ class GraphScriptTestCase(TestCase):
         compute = Compute.objects.create(name="gs", hostname="192.0.2.1", login="u", password="p", type=1)
         with patch("computes.views.wvmHostDetails") as details, patch.object(
             Compute, "status", new_callable=PropertyMock, return_value=True
-        ), patch.object(Compute, "capacity", new=None):
+        ), patch.object(Compute, "capacity", new=None), patch("computes.views.host_pools", return_value=None):
             details.return_value.get_node_info.return_value = ("h", "x86_64", 1024, 2, "cpu", "qemu+tcp://h/system")
             details.return_value.get_cpu_topology.return_value = TOPOLOGY
             page = self.client.get(reverse("overview", args=[compute.id])).content.decode()