[cinder] setting `rbd_exclusive_cinder_pool = True` with multiple cinder-volume writing to the same pool

Hi, Just doing a quick sanity check - I can set `rbd_exclusive_cinder_pool = True` (in pike, where the change landed first) even if more than one cinder-volume is writing to the same Ceph pool, right? Assuming nothing writes to the pool outside of cinder, we should be good as far as I understand the code. -Chris