Make identity v2 tenants_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 identity v2 tenant_client use **kwargs.

Partially implements blueprint consistent-service-method-names

Change-Id: I3fe7b6b7f81a0b20888b2c70a717065e4b43674f
6 files changed