Do not wait for neutron event if not powering on libvirt domain

When resizing/migrating a stopped instance, the power_on flag is False
in _create_domain_and_network so virtual interfaces are not plugged and
we are waiting for an event callback from Neutron that won't happen.
This leads to an eventlet timeout and subsequent attempt to destroy the
non-running domain, which results in a libvirtError.

This change just adds the power_on flag to the list of conditions for
determining if we should wait for an event callback from Neutron.

Closes-Bug: #1321872

Change-Id: Id87ed125db8b1e807b7fa0d99180d0820edbed3e
(cherry picked from commit e0228eb7e739956978f002f58edf35bc4d698022)
Merge "Do not wait for neutron event if not powering on libvirt domain" into stable/icehouse