Provide a "--local" flag to "bin/conduit call" to force in-process execution

Summary:
See PHI1692. Currently, it's hard to get a local profile or "--trace" of some Diffusion API methods, since they always proxy via HTTP -- even if the local node can serve the request.

This always-proxy behavior is intentional (so we always go down the same code path, to limit surprises) but inconvenient when debugging. Allow an operator to connect to a node which can serve a request and issue a `--local` call to force in-process execution.

This makes it straightforward to "--trace" or "--xprofile" the call.

Test Plan: Ran `bin/conduit call ...` with and without `--local` using a Diffusion method on a clustered repository. Without `--local`, saw proxy via HTTP. With `--local`, saw in-process execution.

Differential Revision: https://secure.phabricator.com/D21114

src/applications/conduit/management/PhabricatorConduitCallManagementWorkflow.php

@@ -21,6 +21,12 @@ final class PhabricatorConduitCallManagementWorkflow
               'File to read parameters from, or "-" to read from '.
               'stdin.'),
           ),
+          array(
+            'name' => 'local',
+            'help' => pht(
+              'Force the request to execute in this process, rather than '.
+              'proxying to another host in the cluster.'),
+          ),
           array(
             'name' => 'as',
             'param' => 'username',
@@ -75,9 +81,17 @@ final class PhabricatorConduitCallManagementWorkflow
 
     $params = phutil_json_decode($input_json);
 
-    $result = id(new ConduitCall($method, $params))
-      ->setUser($actor)
-      ->execute();
+    $call = id(new ConduitCall($method, $params))
+      ->setUser($actor);
+
+    $api_request = $call->getAPIRequest();
+
+    $is_local = $args->getArg('local');
+    if ($is_local) {
+      $api_request->setIsClusterRequest(true);
+    }
+
+    $result = $call->execute();
 
     $output = array(
       'result' => $result,