LU-8465 e2fsck: optimize the inserting of dir_info_db

LU-8465 e2fsck: optimize the inserting of dir_info_db

Binary search is now used when inserting an dir info to the array.
Memmove is now used when moving array. Both of them improves
the performance of inserting.

This patch is also a prepartion for the merging of two dir db
arrays.

Change-Id: Iefcf64f195ae6c2f85ac3d550863cfd06815037e
Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/36004
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>