Previously, there was a disagreement between WFE and CA as to what the correct
issuer certificate was. Consolidate on test-ca2.pem (h2ppy h2cker fake CA).
Also, the CA configs contained an outdated entry for "IssuerCert", which was not
being used: The CA configs now use an "Issuers" array to allow signing by
multiple issuer certificates at once (for instance when rolling intermediates).
Removed this outdated entry, and the config code for CA to load it. I've
confirmed these changes match what is currently in production.
Added an integration test to check for this problem in the future.
Fixes#3309, thanks to @icing for bringing the issue to our attention!
This also includes changes from #3321 to clarify certificates for WFE.
827f7859f2