Fixed lp:1382709: openstack provider now returns SHUTOFF and SUSPENDED instances as well

This fixes http://pad.lv/1382709. When an OpenStack instance
managed by Juju is manually stopped or suspended, its state
changes to SHUTOFF or SUSPENDED, respectively. Because the
openstack provider does not return details for instances
with states other than ACTIVE, BUILD, or BUILD(spawning),
the instance updater worker will fail to retrieve the status
of a manually stopped or suspended instance (there is a warning
in the log instead, which is misleading, as it says "unknown
instance id").

With this patch, instance updater will properly refresh the status
of such instances, after the LongPoll interval (15m) has passed.