share groups api does not support AZs

[Valeriy Ponomaryov]

API for share groups does not support setting "availability zone". Also, DB model does not have appropriate field. BUT, its support stated in spec [1] and supported by client:

$ manila help share-group-create
usage: manila share-group-create [--name <name>] [--description <description>]
                                 [--share-types <share_types>]
                                 [--share-group-type <share_group_type>]
                                 [--share-network <share_network>]
                                 [--source-share-group-snapshot <source_share_group_snapshot>]
                                 [--availability-zone <availability-zone>]

Creates a new share group (Experimental).

Optional arguments:
  --name <name> Optional share group name. (Default=None)
  --description <description>
                        Optional share group description. (Default=None)
  --share-types <share_types>, --share_types <share_types>
                        Comma-separated list of share types. (Default=None)
  --share-group-type <share_group_type>, --share_group_type <share_group_type>, --type <share_group_type>
                        Share group type name or ID of the share group to be
                        created. (Default=None)
  --share-network <share_network>, --share_network <share_network>
                        Specify share network name or id.
  --source-share-group-snapshot <source_share_group_snapshot>, --source_share_group_snapshot <source_share_group_snapshot>
                        Optional share group snapshot name or ID to create the
                        share group from. (Default=None)
  --availability-zone <availability-zone>, --availability_zone <availability-zone>, --az <availability-zone>
                        Optional availability zone in which group should be
                        created. (Default=None)

And attempt to create share group with AZ returns error code 400 and following message:

$ manila -d share-group-create --name az1 --availability-zone nova
...
REQ: curl -i -X POST http://%server-ip%:8786/v2/%project-id%/share-groups -H "Accept: application/json" -H "X-Auth-Token: %token%" -H "X-Openstack-Manila-Api-Version: 2.32" -H "X-OpenStack-Manila-API-Experimental: true" -H "User-Agent: python-manilaclient" -H "Content-Type: application/json" -d '{"share_group": {"name": "az1", "availability_zone": "nova"}}'

RESP: [400] {'Content-Length': '95', 'X-Compute-Request-Id': 'req-%some-id%', 'Vary': 'X-OpenStack-Manila-API-Version', 'Connection': 'close', 'X-Openstack-Manila-Api-Version': '2.32', 'Date': 'Wed, 08 Feb 2017 11:55:35 GMT', 'X-Openstack-Manila-Api-Experimental': 'True', 'Content-Type': 'application/json; charset=UTF-8'}
RESP BODY: {"badRequest": {"message": "The fields set([u'availability_zone']) are invalid.", "code": 400}}
...

[1] https://github.com/openstack/manila-specs/blob/master/specs/ocata/manila-share-groups.rst#rest-api-impact