libext2fs: quiet spurious group checksum errors

libext2fs: quiet spurious group checksum errors

If we have to read the backup group descriptor checksums, the UNINIT
flags are cleared to ensure that all of the inodes in the filesystem
are scanned.  However, the code that reset the UNINIT flags did not
reset the group checksum, and this produced many spurious error
messages in e2fsck.

Group descriptor 0 checksum is invalid.  FIXED.
Group descriptor 1 checksum is invalid.  FIXED.
:
:

Recompute checksums after modifying group descriptors to avoid these
error messages.  Remove expected error messages in f_illitable_flexbg.

Signed-off-by: Andreas Dilger <adilger@whamcloud.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>