Don't define virsh secret if already defined

We test to see if the ceph secret already has been defined before
installing the secret again.

This is mainly done to keep our Foreman runs clean, as it reports
on hosts that have had changes applied. Without the 'unless' clause
any node that has the nova compute class installed will report as
having changes applied.

Change-Id: I05e83f07570d4a0e67a700bd9d9030eef1c261c3
Merge "Don't define virsh secret if already defined"