Ensure that device paths provided by end users are used for OSD's,
rather than the link target device as this may change between
reboots. The specific use case is bcache, where:
/dev/bcacheX:
changes between reboots
/dev/disk/by-dname/bcacheX:
udev managed and consistent
This change also ensures that any unit data is updated to switch
back to using the provided block device path, rather than the
actual target which may have been used in prior charm revisions.
Change-Id: If5e88d93b9323052ea762d3a4b66f2442d4a19be
Depends-On: If0e1fbc62bfe7d0f9e21db9bfdeee761060de846
Closes-Bug: 1782439
488f7dffef