btrfs: qgroup handling on data extents balance

btrfs: qgroup handling on data extents balance

Btrfs after v4.2 kernel will leaks qgroup numbers for relocated data
extents, due to the design of tree block direct swap.

This test case will check if such data balance will corrupt qgroup.

Reported-by: Mark Fasheh <mfasheh@suse.de>
Reported-by: Filipe Manana <fdmanana@gmail.com>
Signed-off-by: Qu Wenruo <quwenruo@cn.fujitsu.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>