Fix file location for nova compute rbd secret

The rbd secret location was mixed between /etc/nova
and /etc/ceph. This patch changes the secret to
be in /etc/nova for both the file and exec
resources so that virsh secrets are set correctly

Change-Id: I50f0324d911f20d5a072c769edcf289ae59f817a
Merge "Fix file location for nova compute rbd secret"