Add Sahara plugins list as a configurable parameter
Add Sahara plugins list as a configurable parameter

The hardcoded list should be configurable, and defaulted
to their current value.

Change-Id: I517aa61f21c6f4d0975b10a7aa85177c543487e0
Closes-bug: 1560098

openstack/tripleo-heat-templates,dprince/tripleo-heat-templates,openstack/tripleo-heat-templates,dprince/tripleo-heat-templates