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

Partially implements blueprint consistent-service-method-names

Change-Id: If9770e07af68b5dfd8035f731b798067df4b59b3
2 files changed