Adding unit testing station to workflow

Adds unittest function to worker to invoke a docker
container to pull user code and run a user-specified
testing tool ("tox -epy27") against the code.

Until Mistral is used for stage control flow, these
stages pass messages to the next stage as necessary.
Of special note is build calling unittest directly,
and build calling deploy itself. These calls will likely
be removed as workflows shoulder this work when Mistral
is fully integrated.

Change-Id: I94073bc5e46a1a3ed663c79d93f985c1566024fe