[BB-3686] Change ANSIBLE_APPSERVER_REQUIREMENTS_PATH to requirements_ansible_2.8.17.txt

[0x29a]

Changes ANSIBLE_APPSERVER_REQUIREMENTS_PATH to requirements_ansible_2.8.17.txt and adds migration to update default value in the database.

Currently, when we want to run koa/master Open edX app server, we have to use a separate branch from ansible-playbooks repo. So, we always need to rebase this branch from master. This PR solves this issue and enables Ansible 2.8.17 for appserver.yml playbook by default.

With fixes that are already merged in master, Ansible 2.8.17 has proven to be stable for Ubuntu 16.04 and 20.04, so this change is safe.

JIRA tickets:

• BB-3686

Dependencies:

• Depends on [BB-3686] Create separate requirements file for Ansible 2.8.17 ansible-playbooks#202.

Testing instructions:

1. Attach to the stage Ocim screen, and switch window to bash.
2. Checkout branch to 0x29a/bb3686/change_default_appserver_requirements_file.
3. Switch window to ipython and restart the shell.
4. Ensure that settings.ANSIBLE_APPSERVER_REQUIREMENTS_PATH equals to requirements_ansible_2.8.17.txt.
5. Switch window to bash and run make migrate.
6. After migration is finished, switch back to ipython window and create test instance: production_instance_factory(sub_domain='bb3686').
7. Go to https://stage.manage.opencraft.com/admin/, open settings for the instance with bb3686 sub-domain.
8. You should see that Ansible appserver requirements path is equal to requirements_ansible_2.8.17.txt.
9. Change Ansible appserver version to 0x29a/bb3686/separe_requirements_file_for_ansible2.8.17.
10. Leave Openstack server base image as is. Our goal is to check that everything works for current default release, juniper.3.
11. Create app server for this instance and ensure that it provisioned fine.

Reviewers

• @shimulch

[0x29a]

Test failure is expected, since there is no straightforward way of changing appserver's setting. Test will pass after merging related PR against ansible-playbooks.

[shimulch]

LGTM 👍

• I tested this on the deployed app server and instance in the stage.
• I read through the code
• [N/A] I checked for accessibility issues
• [N/A] Includes documentation
• [N/A] I made sure any change in configuration variables is reflected in the corresponding client's configuration-secure repository.