The VM page reads the VM from libvirt throughout. When its host could
not be reached, the connection error replaced the page with the error
page and showed libvirt's message, which names the host and how it is
reached, to any user who may view the VM.
The page now checks Compute.status first. If the host is not connected,
it goes to the instance list with a message: administrators (superuser
or view_instances) get the host and the error, other users only that
the VM's host cannot be reached right now. The list shows the VM as
unknown.
This covers the page itself; actions on the VM still report libvirt's
error if the host drops. The detail page tests now mock a connected
host.
Checked against the test hosts: a real VM's page opens as before, a VM
on an unreachable compute leads to the list with the user's or the
administrator's message. The new tests fail on the previous code.
The console settings form on the VM detail page renders the VNC password
(PasswordInput(render_value=True)) and was shown to every is_staff user.
A staff user with the global view_instances permission, or a staff owner
without is_vnc, could read the VNC password of every VM they could see.
Add instances.utils.can_manage_console (active superuser, or an active
owner with is_change and is_vnc), which matches what update_console
already enforced. The detail view only builds the form, and so only puts
the password into the page, when it returns True; the template and
update_console use the same rule.
