Dockerize tests

[ryansanford]

Here's the skeleton for dockerized tests for review tomorrow.

Things I'm explicitly seeking buy-in on. not married to existing implementation, but wanted to do something for sake of discussion:

• TEST_ARGS pass-through options for docker/test.sh to test/bin/test.sh
• Cache orthanc docker image. (45s on travis with no caching)
• level of input validation appropriate. I'd prefer more extensive
• location of docker/test.sh. This still feels awkward to me. If I'm new to a repo, I expect to find test convience scripts in test/bin. Maybe this is wrong and I need to get over this?
• WIP...

[ryansanford]

@gsfr Heads up

[gsfr]

@ryansanford Per offline discussion, please minimize orthanc-config.json and rename test directory to tests to avoid bash keyword conflict.