Extend all "ManagementWorkflow" classes from a base class

Summary:
Ref T2015. Not directly related to Drydock, but I've wanted to do this for a bit.

Introduce a common base class for all the workflows in the scripts in `bin/*`. This slightly reduces code duplication by moving `isExecutable()` to the base, but also provides `getViewer()`. This is a little nicer than `PhabricatorUser::getOmnipotentUser()` and gives us a layer of indirection if we ever want to introduce more general viewer mechanisms in scripts.

Test Plan: Lint; ran some of the scripts.

Reviewers: btrahan

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T2015

Differential Revision: https://secure.phabricator.com/D7838

src/applications/files/management/PhabricatorFilesManagementWorkflow.php

@@ -1,11 +1,7 @@
 <?php
 
 abstract class PhabricatorFilesManagementWorkflow
-  extends PhutilArgumentWorkflow {
-
-  public function isExecutable() {
-    return true;
-  }
+  extends PhabricatorManagementWorkflow {
 
   protected function buildIterator(PhutilArgumentParser $args) {
     $names = $args->getArg('names');
@@ -20,7 +16,7 @@ abstract class PhabricatorFilesManagementWorkflow
 
     if ($names) {
       $query = id(new PhabricatorObjectQuery())
-        ->setViewer(PhabricatorUser::getOmnipotentUser())
+        ->setViewer($this->getViewer())
         ->withNames($names)
         ->withTypes(array(PhabricatorFilePHIDTypeFile::TYPECONST));