utils_misc: Update mount check function

When do mount check, the nfs type displays as 'nfs4' if mount
version 4 NFS server, so using regex to search the mount items.
NFS not mount is not an error, so change it to debug level.

Remove umount step as it's not make sense to do umount in mount
function.

BTW, disable verbose by default for mount/umount/is_mount functions.

Signed-off-by: Yanbing Du <ydu@redhat.com>