Make v3 update_role use **kwargs & doc string

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 update_role of v3 identity_client use **kwargs.
Also update doc string for the same.

Partially implements blueprint consistent-service-method-names

Change-Id: Ic30ce16d5240e597b5abab1590fbfa251321f2b1
2 files changed