Actually check the error on obtaining lock during removal.
Actually check the error on obtaining lock during removal.

yp-engineering/rbd-docker-plugin,porcupie/rbd-docker-plugin,yybear/rbd-docker-plugin,clinta/rbd-docker-plugin,yp-engineering/rbd-docker-plugin,opskumu/rbd-docker-plugin,clinta/rbd-docker-plugin,porcupie/rbd-docker-plugin,opskumu/rbd-docker-plugin,yybear/rbd-docker-plugin