ceph: skip ceph/001-ceph/003 if test_dummy_encryption is enabled.

Some tests on ceph require changing the layout of new files, which is
forbidden when the files are encrypted. Skip these tests if the
test_dummy_encryption mount option is being used.

Cc: Luis Henriques <lhenriques@suse.de>
Signed-off-by: Jeff Layton <jlayton@kernel.org>