Update mount check function

1. 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.
2. It's not make sense to do umount in a mount function.

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