libmount: fix regression test helper

Signed-off-by: Ondrej Oprala <ondrej.oprala@gmail.com>
Signed-off-by: Karel Zak <kzak@redhat.com>
libmount: read optional mountinfo fields

[kzak@redhat.com: - rename struct member and functions from
                    "propagation" to "optional fields"
                  - split the original patch
                  - fix parser]

Signed-off-by: Ondrej Oprala <ondrej.oprala@gmail.com>
Signed-off-by: Karel Zak <kzak@redhat.com>
findmnt: add OPT-FIELDS column

Signed-off-by: Karel Zak <kzak@redhat.com>
findmnt: add ID column

Signed-off-by: Karel Zak <kzak@redhat.com>
libmount: add mnt_fs_get_propagation()

Signed-off-by: Karel Zak <kzak@redhat.com>
findmnt: add PROPAGATION column

Signed-off-by: Karel Zak <kzak@redhat.com>