In _get_instance_capabilities() we get a list of host capabilities and then
build a list of arches supported by the virt type of an instance to arrive
at the list of possibilities for the instance. We check each of those
against our enum, but fail to gracefully skip unsupported values should we
encounter one.
This patch makes that graceful, and also introduces an unsupported arch to
the test stub to make sure we always skip it. Note that we do not warn
because this happens once per instance in a periodic task, and since the
situation is caused by a (somewhat permanent) mismatch of libvirt and
nova version support, isn't something that needs to be remedied by an
operator.
Closes-Bug: #1820125
Change-Id: I5d95bd50279a6bf903a5793ad5f3ae9d06f085f4
71df650d0a