mail: make status a tristate

status can be 'passed', 'failed' or 'skipped'. The motivation for this
change is that when using a relay, we can provide a message indicating
why the check was skipped.

dashboard/src/views/EmailStatusView.vue

@@ -31,9 +31,7 @@ async function refreshStatus(domain) {
     console.error(error);
   } else {
     domain.status = Object.keys(result).every((k) => {
-      if (k === 'dns') return Object.keys(result.dns).every(function (k) { return result.dns[k].status; });
-      if (!('status' in result[k])) return true; // if status is not present, the test was not run
-      return result[k].status;
+      return result[k].status === 'passed' || result[k].status === 'skipped';
     });
     domain.statusCheckDone = true;
   }