rbd: enabling/disabling rbd feature should report missing dependency

rbd: enabling/disabling rbd feature should report missing dependency

Currently while enabling or disabling rbd feature command does not
give missing dependency for eg: attempting to enable the journaling
feature on an image that doesn't have the exclusive-lock feature
enabled should give missing dependency error message.

Fixes: http://tracker.ceph.com/issues/16985
Reported-by:  Jason Dillaman <dillaman@redhat.com>
Signed-off-by: Gaurav Kumar Garg <garg.gaurav52@gmail.com>