Test script for CRUD operations on regions

Adds test_regions.py test script to identity v3.
Also adds related XML and JSON supporting methos in client file
region_client.py. Modified the identity base.py and common file
clients.py with details about region_client.
The test cases in the test script are
test_create_update_get_delete_region,
test_create_region_with_specific_id and
test_list_regions.

Change-Id: Ib0f07d04f6c31729bacdcfde065777e64fb76333
Use correct base test class for test_stress unit tests

This commit switches the stress test unit tests to use the correct
base test class. It was previously using the tempest test base test
class instead of the unit test one.

Change-Id: I518d5b50abbd8c54335e7d5f1a53e0c1b6e36673
Merge "Test script for CRUD operations on regions"