Allow the omnipotent viewer to see objects in uninstalled applications

Particularly, in the cluster, it needs to be able to see Almanac services.
This permission may be conflated with the logged-out viewer, since neither
have PHIDs.

Auditors: btrahan

src/applications/base/PhabricatorApplication.php

@@ -449,6 +449,10 @@ abstract class PhabricatorApplication
     $class,
     PhabricatorUser $viewer) {
 
+    if ($viewer->isOmnipotent()) {
+      return true;
+    }
+
     $cache = PhabricatorCaches::getRequestCache();
     $viewer_phid = $viewer->getPHID();
     $key = 'app.'.$class.'.installed.'.$viewer_phid;