core: Add --tar-autocreate-parents option for commit

The tar files we're making of artifacts don't include parent
directories.  Now we could change the builder to make them, but we can
also just autocreate them on import.  Mode 0755 with no xattrs seems
OK here.

tests/t0006-libarchive.sh

@@ -100,3 +100,13 @@ assert_file_has_content otherfile "not overwritten"
 assert_file_has_content subdir/original "original"
 assert_file_has_content subdir/new "new"
 echo "ok tar multicommit contents"
+
+cd ${test_tmpdir}/multicommit-files
+tar -c -C files1 -z -f partial.tar.gz subdir/original
+$OSTREE commit -s 'partial' -b partial --tar-autocreate-parents --tree=tar=partial.tar.gz
+echo "ok tar partial commit"
+
+cd ${test_tmpdir}
+$OSTREE checkout partial partial-checkout
+cd partial-checkout
+assert_file_has_content subdir/original "original"