feat(machine): Poll for machine state on each heartbeat

* Refactor Machine into Machine with static/dynamic MachineStates
* Refresh dynamic MachineState before pushing state to Registry
* Replace references to machine name with bootid
refactor(AgentState): Rename GetUnbadeOffers -> GetOffersWithoutBids
refactor(AgentState): Drop unused method GetBadeOffers
fix(fleetctl): Only set default --tunnel port if value provided
fix(systemd): panic when unable to connect to dbus
Merge pull request #118 from bcwaldon/fix-96

feat(machine): Poll for machine state on each heartbeat