fsck: create a tombstone when the parent is missing
fsck: create a tombstone when the parent is missing

Change the previous logic that a tombstone commit was created when
a partialcommit is found.

Signed-off-by: Giuseppe Scrivano <20002b7b24c75512093a71a58285826d5c504fca@redhat.com>

GNOME/ostree,GNOME/ostree,gatispaeglis/ostree,gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree,gatispaeglis/ostree,gatispaeglis/ostree,GNOME/ostree,gatispaeglis/ostree,GNOME/ostree