Add PROPEL_PDO_CONNECTION_TIMEOUT env variable

With the PropelBundle Symfony integration there is no way to correctly specify PDO attributes.
The configuration schema requires a scalar value, however Propel requires a keyed 'value' array.
This allows us to specify the timeout within the runtime environment (i.e for Lambda).

runtime/lib/Propel.php

@@ -686,6 +686,13 @@ public static function initConnection($conparams, $name, $defaultClass = Propel:
             $con = new $classname($dsn, $user, $password, $driver_options);
             $con->setAttribute(PDO::ATTR_ERRMODE, PDO::ERRMODE_EXCEPTION);
             $con->setAttribute(PropelPDO::PROPEL_ATTR_CONNECTION_NAME, $name);
+
+            // With the PropelBundle Symfony integration there is no way to correctly specify PDO attributes.
+            // The configuration schema requires a scalar value, however Propel requires a keyed 'value' array.
+            // This allows us to specify the timeout within the runtime environment (i.e for Lambda).
+            if ($connectionTimeout = \getenv('PROPEL_PDO_CONNECTION_TIMEOUT')) {
+                $con->setAttribute(\PDO::ATTR_TIMEOUT, $connectionTimeout);
+            }
         } catch (PDOException $e) {
             throw new PropelException("Unable to open PDO connection", $e);
         }