Make docker build's devstack.yml a symlink to the playbook version.

docker/build/edxapp/devstack.yml

----
-# The only difference between these requirements and the role defaults is the
-# presence of the "development.txt" and "testing.txt" files. These two sets
-# of requirements should not be used in production.
-development_requirements_file:   "{{ edxapp_code_dir }}/requirements/edx/development.txt"
-testing_requirements_file:   "{{ edxapp_code_dir }}/requirements/edx/testing.txt"
-
-edxapp_requirements_files:
-  - "{{ pre_requirements_file }}"
-  - "{{ github_requirements_file }}"
-  - "{{ custom_requirements_file }}"
-  - "{{ local_requirements_file }}"
-  - "{{ base_requirements_file }}"
-  - "{{ post_requirements_file }}"
-  - "{{ paver_requirements_file }}"
-  - "{{ development_requirements_file }}"
-  - "{{ testing_requirements_file }}"

docker/build/edxapp/devstack.yml

+../../../playbooks/roles/edxapp/vars/devstack.yml
\ No newline at end of file

playbooks/roles/edxapp/vars/devstack.yml

@@ -2,13 +2,6 @@
 # The only difference between these requirements and the role defaults is the
 # presence of the "development.txt" and "testing.txt" files. These two sets
 # of requirements should not be used in production.
-pre_requirements_file:    "{{ edxapp_code_dir }}/requirements/edx/pre.txt"
-github_requirements_file: "{{ edxapp_code_dir }}/requirements/edx/github.txt"
-custom_requirements_file:   "{{ edxapp_code_dir }}/requirements/edx/custom.txt"
-local_requirements_file:  "{{ edxapp_code_dir }}/requirements/edx/local.txt"
-base_requirements_file:   "{{ edxapp_code_dir }}/requirements/edx/base.txt"
-post_requirements_file:   "{{ edxapp_code_dir }}/requirements/edx/post.txt"
-paver_requirements_file:   "{{ edxapp_code_dir }}/requirements/edx/paver.txt"
 development_requirements_file:   "{{ edxapp_code_dir }}/requirements/edx/development.txt"
 testing_requirements_file:   "{{ edxapp_code_dir }}/requirements/edx/testing.txt"