CLOUDSTACK-4225: change to directory where snapshots are mounted

return back to HOME_DIR and unmount the secondary storage

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
(cherry picked from commit 99329dfa4a4298a57245e224b533d0201e83f7c8)
Add more debug logging to download detached volume test

Signed-off-by: Prasanna Santhanam <tsp@apache.org>
(cherry picked from commit 3455a76237481c3bbb590e88d37b6ca351c113fc)