Make install of post.txt optional for jenkins_worker.

playbooks/roles/jenkins_worker/tasks/python.yml

@@ -58,10 +58,29 @@
     - pre.txt
     - github.txt
     - base.txt
-    - post.txt
     - paver.txt
   sudo_user: "{{ jenkins_user }}"
 
+
+# These and the pip install below it can be removed some time after
+# https://github.com/edx/edx-platform/pull/7465 has merged.
+# This will keep us from breaking after that gets merged.
+- stat: path="{{ jenkins_home }}/shallow-clone/requirements/edx/post.txt"
+  register: post_requirements
+  sudo_user: "{{ jenkins_user }}"
+
+- name: Install edx-platform post requirements using pip
+  pip: >
+    requirements={{ jenkins_home }}/shallow-clone/requirements/edx/{{ item }}
+    extra_args="--exists-action=w"
+    virtualenv={{ jenkins_home }}/edx-venv
+    virtualenv_command=virtualenv-2.7
+    executable=pip
+  with_items:
+    - post.txt
+  sudo_user: "{{ jenkins_user }}"
+  when: post_requirements.stat.exists
+
 # Archive the current state of the virtualenv
 # as a starting point for new builds.
 # The edx-venv directory is deleted and then recreated