Add support for LocalConnector type in brick

GPFS and other file based drivers require a LocalConnector to support
volume connection and migration operations.

Modify brick/initiator/connector.py to add LocalConnector class.

Modify test_brick_connector.py to extend test_factory to include LocalConnector
class.

Modify test_gpfs.py to include new migrate_volume test.

Modify test_utils.py to extend test_brick_get_connector to include LocalConnector
class.

Closes-Bug: #1218052

Change-Id: I259fae339c2df7ae304a91c80c27d135762041f5