LU-8465 e2fsck: serialize fix operations

LU-8465 e2fsck: serialize fix operations

Allow different threads to fix at the same time could
be dangerous and error-prone now, and most of time
parallel scanning and checking is important.

So this patch adds a mutex to serialize
fix operations during pass1.

And the good benefit of this, we don't need block
allocations and free, superblock updates protection
any more, since only fix operations during pass1
could touch them.

Change-Id: Id19a54db86820d7c50e4b84ad10b2e3cb9d1ff2b
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/37826
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>