e2fsck: copy bitmaps when copying context

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.

E2fsprogs-commit: 4d47d0e84388bdf2242e09f9ba592ea778c1ba8e

Change-Id: I6a5a2b49b845215a7a735a828709396586520536
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>