When cluster.databases is configured, read the master connection from it

Summary:
Ref T4571. Ref T10759. Ref T10758. This isn't complete, but gets most of the job done:

  - When `cluster.databases` is set up, most things ignore `mysql.host` now.
  - You can `bin/storage upgrade` and stuff works.
  - You can browse around in the web UI and stuff works.

There's still a lot of weird tricky stuff to navigate, and this has real no advantages over configuring a single server yet (no automatic failover, etc).

Test Plan:
  - Configured `cluster.databases` to point at my `t1.micro` hosts in EC2 (master + replica).
  - Ran `bin/storage upgrade`, got a new install setup on them properly.
  - Survived setup warnings, browsed around.
  - Switched back to local config, ran `bin/storage upgrade`, browsed around, went through setup checks.
  - Intentionally broke config (bad hosts, no masters) and things seemed to react reasonably well.

Reviewers: chad

Reviewed By: chad

Maniphest Tasks: T4571, T10758, T10759

Differential Revision: https://secure.phabricator.com/D15668

src/infrastructure/cluster/PhabricatorDatabaseRef.php

@@ -239,7 +239,7 @@ final class PhabricatorDatabaseRef
         continue;
       }
 
-      $conn = $ref->newConnection();
+      $conn = $ref->newManagementConnection();
 
       $t_start = microtime(true);
       try {
@@ -303,18 +303,69 @@ final class PhabricatorDatabaseRef
     return $refs;
   }
 
-  protected function newConnection() {
+  public function newManagementConnection() {
+    return $this->newConnection(
+      array(
+        'retries' => 0,
+        'timeout' => 3,
+      ));
+  }
+
+  public function newApplicationConnection($database) {
+    return $this->newConnection(
+      array(
+        'database' => $database,
+      ));
+  }
+
+  public static function getMasterDatabaseRef() {
+    $refs = self::loadAll();
+
+    if (!$refs) {
+      $conf = PhabricatorEnv::newObjectFromConfig(
+        'mysql.configuration-provider',
+        array(null, 'w', null));
+
+      return id(new self())
+        ->setHost($conf->getHost())
+        ->setPort($conf->getPort())
+        ->setUser($conf->getUser())
+        ->setPass($conf->getPassword())
+        ->setIsMaster(true);
+    }
+
+    $master = null;
+    foreach ($refs as $ref) {
+      if ($ref->getDisabled()) {
+        continue;
+      }
+      if ($ref->getIsMaster()) {
+        return $ref;
+      }
+    }
+
+    return null;
+  }
+
+  private function newConnection(array $options) {
+    $spec = $options + array(
+      'user' => $this->getUser(),
+      'pass' => $this->getPass(),
+      'host' => $this->getHost(),
+      'port' => $this->getPort(),
+      'database' => null,
+      'retries' => 3,
+      'timeout' => 15,
+    );
+
+    // TODO: Remove this once the MySQL connector has proper support
+    // for it, see T6710.
+    ini_set('mysql.connect_timeout', $spec['timeout']);
+
     return PhabricatorEnv::newObjectFromConfig(
       'mysql.implementation',
       array(
-        array(
-          'user'      => $this->getUser(),
-          'pass'      => $this->getPass(),
-          'host'      => $this->getHost(),
-          'port'      => $this->getPort(),
-          'database'  => null,
-          'retries'   => 0,
-        ),
+        $spec,
       ));
   }