tests: add tests for directory entry blocks with checksum errors

Add some regression tests to examine how e2fsck handles directory
entry blocks and htree blocks with (a) malformed directory entries;
(b) incorrect checksums; or (c) obviously garbage entries.

Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Signed-off-by: Theodore Ts'o <tytso@mit.edu>
8 files changed