btrfs: add test for zone auto reclaim

btrfs: add test for zone auto reclaim

Add a test for commit 18bb8bbf13c1 ("btrfs: zoned: automatically
reclaim zones").

This test creates a two file on a newly created FS in a way that
when we delete the first one, an auto reclaim process will be
triggered by the FS.

After the reclaim process, it verifies that the data was moved to
another zone and old zone was successfully reset.

Signed-off-by: Johannes Thumshirn <johannes.thumshirn@wdc.com>
Reviewed-by: Filipe Manana <fdmanana@suse.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>