removing a flavor in use leads to nova api failiure

[David Busby]

More information on this bug may be found a redhat bugzilla here: https://bugzilla.redhat.com/show_bug.cgi?id=836193

In short within the _get_flavor method of compute/views/servers.py if a flavor was removed but an instance is still associated with the removed flavor instance["instance_type"] will return None

As this is not checked before attempting to retrieve the flavour_id this throws a python exception.

[Russell Bryant (russellb)]

This bug was fixed in master by:

    https://review.openstack.org/#/c/8007/

related discussion here:

    https://lists.launchpad.net/openstack/msg12648.html

It's still a problem in Essex (what is in use for this bug). That patch is probably too invasive for a stable branch backport, though.