two small changes for "arc unit" post hook

Summary:
1) unit engine getter method in the unit workflow

   we store some information (unit test results) in the engine that we
   need to access in the "arc unit" post hook

2) make requireCleanWorkingCopy() public

   "arc unit" doesn't need to be clean in general, but we'd like the
   option to upgrade the workflow to require it if necessary.  We use
   this for ensuring a repo is clean before updating unit test
   results.

Test Plan: Used both features in a custom post hook in arc unit

Reviewers: epriestley

Reviewed By: epriestley

CC: dpepper, aran, epriestley

Differential Revision: 917

src/workflow/base/ArcanistBaseWorkflow.php

@@ -573,7 +573,7 @@ class ArcanistBaseWorkflow {
     return empty($this->arguments['allow-untracked']);
   }
 
-  protected function requireCleanWorkingCopy() {
+  public function requireCleanWorkingCopy() {
     $api = $this->getRepositoryAPI();
 
     $working_copy_desc = phutil_console_format(

src/workflow/unit/ArcanistUnitWorkflow.php

@@ -60,6 +60,10 @@ EOTEXT
     return true;
   }
 
+  public function getEngine() {
+    return $this->engine;
+  }
+
   public function run() {
 
     $working_copy = $this->getWorkingCopy();