xfs: xfs_growfs target path must be an active xfs mountpoint

xfs: xfs_growfs target path must be an active xfs mountpoint

xfs_growfs manpage clearly states that the target path must be an
active xfs mountpoint. This is a test to ensure that if the target
path isn't an active xfs mountpoint, the command is rejected. The
purpose is to check the command response, but not necessarily the
functionality of xfs_growfs. Test cases include absolute paths,
relative paths, symbolic links, and bind mounts.

Signed-off-by: Bill O'Donnell <billodo@redhat.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>