add secondary domains

note that for updates to work, we keep the secondary domain optional,
even though they are really not.

part of #809

src/test/common.js

@@ -105,6 +105,7 @@ const app = {
     accessRestriction: null,
     memoryLimit: 0,
     mailboxDomain: domain.domain,
+    secondaryDomains: [],
     redirectDomains: [],
     aliasDomains: []
 };