Like -H, we need to poll every module to check if it is needed
to mount a specific device in '--mount'.
Signed-off-by: Cong Wang <xiyou.wangcong@gmail.com>
btrfsctl is being replaced by the btrfs command in the upstream
tools, so change accordingly. Also, if we're using the btrfs module
we should probably make sure the btrfs driver gets installed.