refactor fake bosh backend
refactor fake bosh backend

[#146717703]

Signed-off-by: Nick Mahoney <37df72260815dd7c7e09de5254fe02d7d2694eb5@pivotal.io>

pivotal-cf-experimental/bosh-bootloader,niroyb/bosh-bootloader,niroyb/bosh-bootloader,pivotal-cf-experimental/bosh-bootloader