Switch to Ansible-free Docker image of credentials

[mumarkhan999]

In order to advance implementation of both OEP-45: Configuring and Operating Open edX and deprecation of the configuration repository, we would like to switch devstack from using primarily Docker images built with Ansible code from the configuration repository to images built from Dockerfiles in each service's repository. We hope this will also help simplify Tutor by providing better base images to derive from, with fewer workarounds and duplicated code blocks required in Tutor.

A/C

• Ensure that the repo's Dockerfile can create a base image which is appropriate for small production installations
• Ensure that the repo's Dockerfile also defines an additional image derived from the base which adds dependencies and configuration changes needed for development environments
• Check with the Tutor developers during code review to see if any further changes to the Dockerfile would help simplify Tutor
• Automate uploads of both images when code changes are merged
• Switch devstack to use the new Ansible-free development image, and do some basic testing to ensure it works before merging