Make volume snapshots_client to 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 volume snapshots_client use **kwargs.

Partially implements blueprint consistent-service-method-names

Change-Id: I1fc18a879702a2f77ebbe704fa2e9c5eaa96b220
9 files changed