LU-456 Force commit to reuse the just-deleted blocks

LU-456 Force commit to reuse the just-deleted blocks

In ext4 non-writeback journal mode, the just-deleted blocks are not
useable until the transaction committed, this could cause filter
return -ENOSPC mistakenly when the just-deleted blocks are not committed.

Whenever block allocation fails for -ENOSPC on filter, we should wait
for the previous deleted blocks committed, then retry the allocation.

Signed-off-by: Niu Yawei <niu@whamcloud.com>
Change-Id: I678b05ae9aa1b9e9d0aa29f48279bc7daedebbb2
Reviewed-on: http://review.whamcloud.com/1022
Tested-by: Hudson
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Reviewed-by: Johann Lombardi <johann@whamcloud.com>
Tested-by: Maloo <whamcloud.maloo@gmail.com>