qtest/ahci: Add migration test

Notes:

 * The migration is performed on QOSState objects.

 * The migration is performed in such a way that it does not assume
   consistency between the allocators attached to each. That is to say,
   you can use each QOSState object completely independently and then at
   an arbitrary point decide to migrate, and the destination object will
   now be consistent with the memory within the source guest. The source
   object that was migrated from will have a completely blank allocator.

ahci-test.c:
 - verify_state is added
 - ahci_migrate is added as a frontend to migrate
 - test_migrate_sanity test case is added.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Message-id: 1430417242-11859-6-git-send-email-jsnow@redhat.com
