fix(api): Support legacyFallback for BUILD_SERVICE (spinnaker#385)

When `service.fiat.legacyFallback` is `true`, this will implicitly allow
access to all build services in the event that `fiat` is unavailable.

fiat-api/src/main/java/com/netflix/spinnaker/fiat/shared/FiatPermissionEvaluator.java

@@ -329,7 +329,7 @@ private boolean permissionContains(UserPermission.View permission,
             .stream()
             .anyMatch(view -> view.getName().equalsIgnoreCase(resourceName));
       case BUILD_SERVICE:
-        return containsAuth.apply(permission.getBuildServices());
+        return permission.isLegacyFallback() || containsAuth.apply(permission.getBuildServices());
       default:
         return false;
     }