(torchx/runtime/hpo) fix ax_test for fb, cleaned up apps/* and added prepend_cwd runopt to local_scheduler + some local scheduler code cleanup (#210)

Summary:
Pull Request resolved: #210

1. Makes ax_test.py work again in sandcastle
2. Clean up `apps/*` directory of unused/empty placeholder modules
3. Add `//torchx/apps:penv` python_binary to be able to deploy apps as penv
4. Add `prepend_cwd` runopt for local scheduler to prepend CWD to replica PATH so that binaries in CWD can take precedence over the ones in PATH (needed to enable ax_test in fb)
5. Some syntactical cleanup for local_scheduler
6. (minimally) deletes base_image (yes it doesn't delete all of it, I'm trying to keep the diff as relevant to enabling ax_test, but had to remove some of it to simplify local_scheduler logic)

Reviewed By: aivanou

Differential Revision: D31262463

fbshipit-source-id: 3f1649e4bc062f3fe6b54f13b03d11b53164fc8d

Author: Kiuk Chung

torchx/apps/__init__.py

@@ -4,7 +4,3 @@
 #
 # This source code is licensed under the BSD-style license found in the
 # LICENSE file in the root directory of this source tree.
-
-from .data import *  # noqa F401
-from .train import *  # noqa F401
-from .hpo import *  # noqa F401

torchx/apps/captum/__init__.py

@@ -0,0 +1,5 @@
+# Copyright (c) Facebook, Inc. and its affiliates.
+# All rights reserved.
+#
+# This source code is licensed under the BSD-style license found in the
+# LICENSE file in the root directory of this source tree.