Fix stuff around mbox header changes

Fix stuff around mbox header changes

Bundle tests got broken after the subject in mbox was changed from the
parsed version to the original one because the tests checked for the
presence of patch's name in the response. Fixing this turned out to be
a bit tricky since the tests check the mbox attachment and HTML
responses separately, so we need a string that would be present in both
(the intuitive idea of checking X-Patchwork-Id won't work well).

Add the patch's name to the content of the test patch so we can continue
testing things the same way, checking for the presence of patch's name.

Also add a releasenote notifying about the inclusion of the original
headers.

Reverts: b2a25342 ("Use parsed subject for mboxes")
Fixes: 01b9cbb9 ("Include all email headers in mboxes")
Signed-off-by: Veronika Kabatova <vkabatov@redhat.com>
Reviewed-by: Stephen Finucane <stephen@that.guru>