When raising a Conduit client exception, show the called method in the error message

Summary: Ref T13581. This message can be slightly more helpful in some cases by showing which method call failed.

Test Plan: Ran `arc branches` under the error condition in D21462, got a more useful error.

Maniphest Tasks: T13581

Differential Revision: https://secure.phabricator.com/D21463

src/conduit/ConduitFuture.php

@@ -62,9 +62,14 @@ final class ConduitFuture extends FutureProxy {
     }
 
     if ($data['error_code']) {
+      $message = pht(
+        '<%s> %s',
+        $this->conduitMethod,
+        $data['error_info']);
+
       throw new ConduitClientException(
         $data['error_code'],
-        $data['error_info']);
+        $message);
     }
 
     $result = $data['result'];