Fix various issues with SSH receivers

Summary:
  - Original command is in SSH_ORIGINAL_COMMAND, not normal argv.
  - Use PhutilShellLexer to parse it.
  - Fix a protocol encoding issue with ConduitSSHWorkflow. I think I'm going to make this protocol accept multiple commands anyway because SSH pipes are crazy expensive to build (even locally, they're ~300ms).

Test Plan: With other changes, successfully executed "arc list --conduit-uri=ssh://localhost:2222".

Reviewers: btrahan, vrana

Reviewed By: btrahan

CC: aran

Maniphest Tasks: T550

Differential Revision: https://secure.phabricator.com/D4232

src/applications/conduit/ssh/ConduitSSHWorkflow.php

@@ -31,9 +31,10 @@ final class ConduitSSHWorkflow extends PhabricatorSSHWorkflow {
       throw new Exception("Invalid JSON input.");
     }
 
-    $params = $raw_params;
+    $params = idx($raw_params, 'params', array());
+    $params = json_decode($params, true);
+    $metadata = idx($params, '__conduit__', array());
     unset($params['__conduit__']);
-    $metadata = idx($raw_params, '__conduit__', array());
 
     $call = null;
     $error_code = null;