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

scripts/ssh/ssh-exec.php

@@ -4,6 +4,10 @@
 $root = dirname(dirname(dirname(__FILE__)));
 require_once $root.'/scripts/__init_script__.php';
 
+$original_command = getenv('SSH_ORIGINAL_COMMAND');
+$original_argv = id(new PhutilShellLexer())->splitArguments($original_command);
+$argv = array_merge($argv, $original_argv);
+
 $args = new PhutilArgumentParser($argv);
 $args->setTagline('receive SSH requests');
 $args->setSynopsis(<<<EOSYNOPSIS
@@ -50,7 +54,7 @@ try {
   // concise/relevant exceptions when the client is a remote SSH.
   $remain = $args->getUnconsumedArgumentVector();
   if (empty($remain)) {
-    throw new Exception("No command.");
+    throw new Exception("No interactive logins.");
   } else {
     $command = head($remain);
     $workflow_names = mpull($workflows, 'getName', 'getName');