reenable boot an instance from a volume

This patch updates our nova boot command to boot
an instance from a volume that is created on
the fly from a Glance image.

The motivation here is to expand our devtest
script so that it has some level of coverage
across Cinder which is commonly broken
in upstream TripleO.

This patch was recently reverted to fix CI... but
was in fact catching a valid Nova upgrade issue:

See https://bugs.launchpad.net/nova/+bug/1354499

Change-Id: I6ba65db401203883b88874f162fa52a5fb522c32
Merge "reenable boot an instance from a volume"