This is to allow operator to prevent enabling redis and/or
etcd from magically configuring cinder coordinator.
Note this change is backwards-compatible.
Change-Id: Ie10be55968e43e3b9cc347b1b58771c1f7b1b910
Related-Bug: #1840070
Signed-off-by: Radosław Piliszek <radoslaw.piliszek@gmail.com>