driver: vmware fusion

[bradrydzewski]

support vmware fusion. The yaml configuration would look something like below. The type parameter would be used to differentiate between vm and container pipelines, and would unmsarshal to a different structure.

---
version: 1
kind: pipeline
type: vmwarefusion

settings:
  image: osx.img

platform:
  os: osx
  arch: amd64

steps:
- name: build
  commands:
  - go build
  - go test