xfstests: btrfs/009: regression test for subvol delete

We were allowing users to delete their default subvolume, which is problematic.
This test is a regression test to make sure we don't let that happen in the
future.  Thanks,

Signed-off-by: Josef Bacik <jbacik@fusionio.com>
Reviewed-by: Eric Sandeen <sandeen@redhat.com>
Signed-off-by: Rich Johnston <rjohnston@sgi.com>

[rjohnston: renumbered test from 003 to 009]

common/rc

@@ -57,6 +57,14 @@ dd()
    fi
 }
 
+_btrfs_get_subvolid()
+{
+	mnt=$1
+	name=$2
+
+	$BTRFS_UTIL_PROG sub list $mnt | grep $name | awk '{ print $2 }'
+}
+
 # Prints the md5 checksum of a given file
 _md5_checksum()
 {