PWX-23689: surface error from Unmount when path is not mounted (#2049)
PWX-23689: surface error from Unmount when path is not mounted (#2049)

We were swallowing the "path not mounted" error in Unmount(). This
prevented the callers from executing the cleanup such as removing
the path. This patch exposes that error.

Signed-off-by: Neelesh Thakur <425f5b533a490f3e45ece49a6c5b6633d2ffcc28@purestorage.com>
libopenstorage/openstorage,libopenstorage/openstorage,libopenstorage/openstorage