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
Merge "Rewrite nova policy to use the new changes of common policy"
Merge "Remove useless codes for server_group"