Fix misleading error message when only cluster database masters are configured

Summary:
Fixes T11446. We can raise the misleading error:

> No valid databases are configured!

...when a valid master is configured but unreachable.

Instead, more carefully raise either "nothing is configured" or "nothing is reachable".

Test Plan: Configured only a master, artificially severed it, got "nothing is reachable" instead of "nothing is configured".

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T11446

Differential Revision: https://secure.phabricator.com/D16386

src/infrastructure/storage/lisk/PhabricatorLiskDAO.php

@@ -122,16 +122,17 @@ abstract class PhabricatorLiskDAO extends LiskDAO {
     }
 
     $replica = PhabricatorDatabaseRef::getReplicaDatabaseRef();
-    if (!$replica) {
+    if ($replica) {
-      throw new Exception(
-        pht('No valid databases are configured!'));
-    }
-
       $connection = $replica->newApplicationConnection($database);
       $connection->setReadOnly(true);
       if ($replica->isReachable($connection)) {
         return $connection;
       }
+    }
+
+    if (!$master && !$replica) {
+      $this->raiseUnconfigured($database);
+    }
 
     $this->raiseUnreachable($database);
   }
@@ -153,10 +154,18 @@ abstract class PhabricatorLiskDAO extends LiskDAO {
         $database));
   }
 
+  private function raiseUnconfigured($database) {
+    throw new Exception(
+      pht(
+        'Unable to establish a connection to any database host '.
+        '(while trying "%s"). No masters or replicas are configured.',
+        $database));
+  }
+
   private function raiseUnreachable($database) {
     throw new PhabricatorClusterStrandedException(
       pht(
-        'Unable to establish a connection to ANY database host '.
+        'Unable to establish a connection to any database host '.
         '(while trying "%s"). All masters and replicas are completely '.
         'unreachable.',
         $database));