Virt: ensure that instance_exists uses objects

Ensure that the method now receives a data object as input.

Change-Id: I6b5a9c9defb61388035ef7d511ccd96998b695aa
Remove useless codes for server_group

Some codes about 'extract_members' from 'create_server_group'
is written in original bp/patch's reviewing
(I650a8f191dea5eab5b4b1828f0b9f65e33edea2a).

But as the design variation, it can't be specified members
in create API (see it in PS29 vs PS30).
But some useless codes are still kept after this feature merged.
So it's necessary to remove them.

Change-Id: I087c8389f2c735a36d656b44c6a3ecfe3a4aa5a3
Closes-Bug: #1325148
libvirt: split and test finish_migration disk resize

Adds a '_disk_resize' method to help resizing disk
by checking and preparing the disk to be extend with disk.api.
Update finish_migration to use this helper.

Closes-Bug: #1298975
Signed-off-by: Sahid Orentino Ferdjaoui <sahid.ferdjaoui@cloudwatt.com>

Change-Id: Iefe16915a2e657d848629d7e4a4fcf67298f913e
Fix InstanceActionEvent traceback parameter not serializable

The change to use InstanceActionEvent in compute.utils.EventReporter
changed the order of how things are done. Before, traceback info were
converted to a string before being sent to the conductor. Now, since
the object method being used remotes itself, the order becomes the
opposite and any captured tracebacks are sent as is, resulting in
errors during messaging.

This adds a serialize_args decorator for this case, which handles
this specific case for the event_finish_with_failure() classmethod.
A more generic approach is needed, and that will be applied to the
also-affected but currently-unused finish_with_failure() instance
method.

Change-Id: Ibedddd606b9d25ffbbb2b1b5358cf0aa4741083f
Co-Authored-By: Dan Smith <dms@danplanet.com>
Closes-Bug: #1317804
Merge "Remove useless codes for server_group"
Merge "libvirt: split and test finish_migration disk resize"
Merge "Virt: ensure that instance_exists uses objects"
Merge "Fix InstanceActionEvent traceback parameter not serializable"