[V3] Make credentials_client use **kwargs

As we discussed on
http://lists.openstack.org/pipermail/openstack-dev/2015-July/068864.html
All http POST/PUT methods need to contain **kwargs as their arguments.
This patch makes credentials_client use **kwargs.

Partially implements blueprint consistent-service-method-names

Change-Id: Icf953bf7234376a877831f88313d935aec25f9bb
2 files changed