Added a new function test for volume type set
Added a new function test for volume type set

This is a new test to validate the setting of one property
for an existing volume type

Change-Id: Ia9a7d86ce9b0d8df9d64ddc1df2d443843bba5ef

redhat-openstack/python-openstackclient,BjoernT/python-openstackclient,openstack/python-openstackclient,openstack/python-openstackclient,dtroyer/python-openstackclient,BjoernT/python-openstackclient,redhat-openstack/python-openstackclient,dtroyer/python-openstackclient