Add kwargs to create_volume in tests/utils.py

Add kwargs to create_volume in tests/utils.py

Add availability_zone parameter and kwargs to make create_volume
function more flexible in order to use this function in
unit tests.
The goal is to remove inner _create_volume function in:
- db/test_transfers.py
- api/contrib/test_backups.py
- test_gpfs.py
- test_volume_transfer.py
- test_volume.py
and to use create_volume from tests/utils instead.

Change-Id: I2d9456ff3ff1cd945042f19c47e40f9f0ec0fe8a