e2fsck: add debug codes for multiple threads

e2fsck: add debug codes for multiple threads

These debug codes are added to run the multiple pass1 check
thread one by one in order. If all the codes are correct,
fsck of multiple threads should have exactly the same outcome
with single thread.

E2fsprogs-commit: a8b483a1e7987a6dddc32bc82db06f649d245630

Change-Id: I41b0493a0cd830b76434ff0f86a87c98d8d3ad22
Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>