Ability to run Augur container as non-root

[JohnStrunk]

Is your feature request related to a problem? If so, please describe the problem:
In order to run Augur on OpenShift, it's necessary to be able to run all the containers as an arbitrary non-root user. This doesn't seem to be a problem for the rabbitmq, postgres, and redis containers, but the actual Augur container won't run as non-root.

Potential solutions:
We should be able to specify an arbitrary user:group in the docker-compose file for the augur service and it should "just work". Ex:

services:
  augur:
    user: 2345:2345  # Run as an arbitrary non-root user

Additional context:
While there are certainly file permission issues:

$ docker logs augur-augur-1
/bin/bash: /entrypoint.sh: Permission denied

there also seem to be path assumptions in the code that will need to be corrected.

Related: #1389

[JohnStrunk]

Feel free to assign this to me.