generic: test XATTR_REPLACE doesn't take the fs down

Kanda Motohiro reported that expanding a tiny xattr into a large
xattr fails on XFS because we remove the tiny xattr from a shortform
fork and then try to re-add it after converting the fork to extents
format having not removed the ATTR_REPLACE flag.  This fails because
the attr is no longer present, causing a fs shutdown.

[Eryu: introduce function "fail" and use it where appropriate]

Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=199119
Reported-by: kanda.motohiro@gmail.com
Signed-off-by: Darrick J. Wong <darrick.wong@oracle.com>
Reviewed-by: Eryu Guan <guaneryu@gmail.com>
Signed-off-by: Eryu Guan <guaneryu@gmail.com>

.gitignore

@@ -52,6 +52,7 @@
 /src/alloc
 /src/append_reader
 /src/append_writer
+/src/attr_replace_test
 /src/attr-list-by-handle-cursor-test
 /src/bstat
 /src/bulkstat_unlink_test