The instance lists read each VM from libvirt while rendering. When that
failed, the libvirt error replaced the whole page with the error page:
one VM removed out of band, or a host that is down, took the index or
a compute's instances page with it. To avoid that, both index views
left out every VM of a host that was not connected, so users saw their
VMs disappear.
- Instance.info is None when the VM cannot be read. The row then shows
the name and owners from the database, the state "Unknown", and no
title, vCPU, memory or actions.
- Both index views list the VMs of a host that is down. The grouped
view marks the host "Not Connected" and leaves out its CPU and memory.
- A compute's instances page shows the connection error, and no longer
says the hypervisor has no instances when it cannot be reached.
Checked against the test hosts with an unreachable compute added: both
index views list its VM as unknown next to the real VMs. The first
load takes 5.5 s (one bounded connection attempt), the next ones
0.1 s. The new tests fail on the previous code (VMs left out, error
pages).
