Change dockerfiles, kubernetes and docker_compose arguments to accept multiple values

[jhrozek]

It's not unusual to have multiple dockerfiles spread around the
codebase, so it would be useful to support that. This patch supports a
JSON-like array e.g. ["Dockerfile", "Dockerfile.dev"].

Fixes: #8

[jhrozek]

@puerco @rdimitrov this is not critical for the release but IMO nice to have. I can't make up my mind about the multi-value strings though..the JSON syntax is kinda obvious but also seems to be a bit ugly.

[puerco]

You mean the yaml in the workflow configuration? I think it's fine as you don't really need to see it unless you need to change the defaults, or change it to this in the example if it seems less ugly?

dockerfiles:
  - "./Dockerfile"
  - "./images"

[jhrozek]

You mean the yaml in the workflow configuration? I think it's fine as you don't really need to see it unless you need to change the defaults, or change it to this in the example if it seems less ugly?

dockerfiles:
  - "./Dockerfile"
  - "./images"

The thing is that the workflows don't seem to support any other configuration type than string, int or bool, at least I don't see it the docs