Support using Docker for running tests

[bradleyfalzon]

Support using Docker for running tests

[bradleyfalzon]

This would potentially have a GopherCI-analyser image which contains all versions of Go (to support #11). The begin with though, it could use golang:1 as the base image and include later versions at a later stage.

The analyser would need to execute multiple commands in the container, such as fetching, running tests, and executing static analysis tools. Each of steps would need to have the output interpreted differently; tests, if they fail, need to be recorded and tools need to pass that output to revgrep.

The container could:

1. execute a script that fetches all dependencies (including vendored #12) and then blocks forever
2. Analyser would then get the container ID
3. Analyser would wait until all dependencies are fetched
4. Other commands could be fed in with a series of docker exec style calls. These could, in some cases be ran concurrently, such as tests and static analysis tools (after fetching has completed). Once completed the container can be terminated and all images removed.
5. Analyser would terminate the container

[bradleyfalzon]

Implemented in 07d248a and docker repo: https://github.com/bradleyfalzon/gopherci-env