Update default Cinder RBD backend_host value
Update default Cinder RBD backend_host value

The Cinder RBD driver's backend_host should use 'cinder::backend_host'
hiera data first, and only use 'cinder::host' if the preferred hiera
value isn't defined.

Partial-Bug: #1753596
Depends-On: I11a55571f4bed630967242c797e08e11c47eab11
Change-Id: I78a88725d297794efd854fbfb14df0611e0e0738

openstack/puppet-tripleo,openstack/puppet-tripleo,openstack/puppet-tripleo