Test live migrate on a paused instance

Nova change Ib38eaf412cb51a9cbfc443c5ec15c5797265ddae adds support for
doing live migration of a paused instance, this adds the test to cover
that scenario.

This also depends on a series of devstack-gate changes to support
multi-host testing in the experimental queue. Specifically, this is
tested in the check-tempest-dsvm-aiopcpu-full job.

Depends-On: I89b7e390bf1cf4f2eccabca2e31a9d1b6b270677

Co-Authored By: "Matthew Gilliard <matthew.gilliard@hp.com>"
Related-Bug: #1305062

Change-Id: I5c6fd3de7ea45d1851bb40037c64ad7fb5e6dc48
3 files changed