Change role to cinder

We slightly miss that fact than cinder should connect to GlusterFS
from node which hosts openstack-cinder-volume service. In our case
it is not controller, but cinder node. So, we just change that role
in tasks.yaml.

Change-Id: Idb055b34e394154bfb2fe1f24ec28edb8a320450
Closes-Bug: #1396996