Uninstall obsolete python packages before installing new ones.

playbooks/roles/edxapp/tasks/deploy.yml

@@ -194,8 +194,18 @@
     - install
     - install:app-requirements
 
+- name: Uninstall obsolete python requirements
+  command: >
+    {{ edxapp_venv_dir}}/bin/paver uninstall_python_packages
+    chdir="{{ edxapp_code_dir }}"
+  sudo_user: "{{ edxapp_user }}"
+  environment: "{{ edxapp_environment }}"
+  tags:
+    - install
+    - install:app-requirements
+
 # Install the python requirements into {{ edxapp_venv_dir }}
-- name : install python requirements
+- name: install python requirements
   # Need to use command rather than pip so that we can maintain the context of our current working directory; some
   # requirements are pathed relative to the edx-platform repo. Using the pip from inside the virtual environment implicitly
   # installs everything into that virtual environment.