generic: test renaming encrypted files without key

generic: test renaming encrypted files without key

Add a new test to test another behavior when accessing encrypted
files without the key: renames should be forbidden, even though they
may be possible cryptographically.  Test both a regular rename and a
cross rename.  (It happens that generic/398 also covers the cross
rename case, but it's primarily for a different reason.)

Cc: Theodore Ts'o <tytso@mit.edu>
Cc: Jaegeuk Kim <jaegeuk@kernel.org>
Cc: Richard Weinberger <richard@nod.at>
Signed-off-by: Eric Biggers <ebiggers@google.com>
Reviewed-by: Eryu Guan <eguan@redhat.com>
Signed-off-by: Eryu Guan <eguan@redhat.com>