LU-8465 e2fsck: copy bitmaps when copying context

LU-8465 e2fsck: copy bitmaps when copying context

This patch copies bitmap when the copying context. In the
multi-thread fsck, each thread use different bitmap that copied
from the glboal bitmap. And Bitmaps from multiple threads will
be merged into a global one after the pass1 finishes.

Change-Id: Ic5e181712630814d12b2fa6e3836ce0acc1832a7
Signed-off-by: Li Xi <lixi@ddn.com>
Signed-off-by: Wang Shilong <wshilong@ddn.com>
Reviewed-on: https://review.whamcloud.com/35712
Tested-by: jenkins <devops@whamcloud.com>
Tested-by: Maloo <maloo@whamcloud.com>
Reviewed-by: Andreas Dilger <adilger@whamcloud.com>