Make create_disk() persistent

Right now a system configured with the ceph plugin will not survive
a reboot because the backing disk we create and mount isn't mounted
at startup, preventing ceph from starting and the rest of nova/glance
from working.

This makes create_disk() idempotently write an fstab rule for the
disk we make, and adds a destroy_disk() handler for cleanup.

Change-Id: I50cd4234f51a335af25be756bd2459dca5aa343c
2 files changed