Remove umount step in mount and update mount check function

1. It's not make sense to do umount in a mount function.
2. When do mount check, the nfs type displays as 'nfs4' if use
   vers=4 nfs server, so using regex to search the mount items.
   Not mount is not an error, so change it to debug level. BTW,
   disable verbose by default.

Signed-off-by: Yanbing Du <ydu@redhat.com>