common: helper to print raw byte output from qgroup show

Newer versions of btrfs-progs change the default output of 'qgroup
show', we have to check what version is running and use the right option
if needed.

Signed-off-by: David Sterba <dsterba@suse.cz>
Signed-off-by: Dave Chinner <david@fromorbit.com>

common/rc

@@ -2799,6 +2799,13 @@ _btrfs_stress_replace()
 	done
 }
 
+# find the right option to force output in bytes, older versions of btrfs-progs
+# print that by default, newer print human readable numbers with unit suffix
+_btrfs_qgroup_units()
+{
+	$BTRFS_UTIL_PROG qgroup show --help 2>&1 | grep -q -- --raw && echo "--raw"
+}
+
 # return device size in kb
 _get_device_size()
 {