Virt: ensure that instance_exists uses objects

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

Change-Id: I6b5a9c9defb61388035ef7d511ccd96998b695aa
Rewrite nova policy to use the new changes of common policy

The oslo has rewritten the common policy for a long time, using a
Enforer class to replace the old check function. In order to sync the
common policy to nova, We have to also changed the nova policy and
related unittests.
Sync policy and relate module from Oslo.
   Some related change-id:Ife909bdf3277ef33c2fb1eae16ae261fa6374c63
                change-id:Ife84189be4b86a3ee90da4539ff2dbed125be23d

Closes-Bug: #1288178

Change-Id: Ic106851a24cfdc9d847f7d0e0d8a6ecbff888e05
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
Revert "Fix migration and instance resize update order"

This reverts commit 6dd5cc503cc05c00c5f9d831480539c67f6e2a48.

Change-Id: Id438276c3d71155ad6a9dfd31280a49e39905ae5
Closes-Bug: #1326778
Merge "Revert "Fix migration and instance resize update order""
Merge "Rewrite nova policy to use the new changes of common policy"
Merge "Remove useless codes for server_group"
Merge "libvirt: split and test finish_migration disk resize"
Merge "Virt: ensure that instance_exists uses objects"