Clarify docstrings for domain flask refactor
Clarify docstrings for domain flask refactor

This change addresses a comment from a previous change[0] to
clarify in the docstring about the APIs that each flask resource
class utilizes from the base class.

[0] https://review.openstack.org/#/c/613182/

Change-Id: Ia21b506726c1f75ff580bddd6b2bf18e2f5660c3

openstack/keystone,mahak/keystone,mahak/keystone,openstack/keystone,mahak/keystone,openstack/keystone