Provide a username and email when running git merge --squash

Summary:
Ref T182. This command should never actually generate a commit because `--squash` prevents that, but `git` seems to sometimes hit a check for username/email configuration (maybe when merging a non-fastforward?).

Give it some dummy values to placate it. This command shouldn't commit anything so these values should never actually be used.

Test Plan: Landed rGITTESTd8c8643cb02bbe60048c6c206afc2940c760a77e.

Reviewers: chad, Mnkras

Reviewed By: Mnkras

Maniphest Tasks: T182

Differential Revision: https://secure.phabricator.com/D14347

src/applications/drydock/blueprint/DrydockWorkingCopyBlueprintImplementation.php

@@ -431,17 +431,28 @@ final class DrydockWorkingCopyBlueprintImplementation
       $src_ref,
       $src_ref);
 
-    $command = csprintf(
+    // NOTE: This can never actually generate a commit because we pass
-      'git merge --no-stat --squash -- %R',
+    // "--squash", but git sometimes runs code to check that a username and
+    // email are configured anyway.
+    $real_command = csprintf(
+      'git -c user.name=%s -c user.email=%s merge --no-stat --squash -- %R',
+      'drydock',
+      'drydock@phabricator',
+      $src_ref);
+
+    // Show the user a simplified command if the operation fails and we need to
+    // report an error.
+    $show_command = csprintf(
+      'git merge --squash -- %R',
       $src_ref);
 
     try {
-      $interface->execx('%C', $command);
+      $interface->execx('%C', $real_command);
     } catch (CommandException $ex) {
       $this->setWorkingCopyVCSErrorFromCommandException(
         $lease,
         self::PHASE_SQUASHMERGE,
-        $command,
+        $show_command,
         $ex);
 
       throw $ex;