e2fsck: serialize fix operations

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.

E2fsprogs-commit: 5485120b668c952b6e83f24a1e1a74eaa7bf362e

Change-Id: Iedb64545240cc9325dc0c4ce737a970b27f4f3f6
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Saranya Muruganandam <saranyamohan@google.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>