Override Docker image command/args at runtime

[bodom0015]

Problem

Our API lets us specify command for an appspec, but this command does not seem to be used when running the container

Overriding the userapp.services.command lets us do this, but it does not automatically use the command from the appspec

In addition, args are completely ignored in the spec

Approach

• Pass args into create_deployment
• Use app_spec command if stack_service does not define one when creating the userapp

How to Test

1. Checkout and run this branch locally
2. Import a new AppSpec the overrides command, for an example see Create heapoverflow.json cheese-hub/catalog#15
   • Note that Various fixes on AddEditSpec page workbench-webui#17 describes a set of changes needed to create this spec using the UI, which is not yet possible
3. Create a new UserApp from this AppSpec (click + on All Apps page or use Swagger UI)
4. Launch the UserApp and wait for it to finish starting up
   • You should see the app turn green in the UI
5. Check kubectl get pods -n <namespace> and make sure container isn't Restarting over and over again