refactor(registry): Rename GetJobs, UpdateJob -> GetMachineJobs, UpdateMachineJob
refactor(registry): Add GetUnscheduledJobs method to Registry

This new method and associated refactoring are in preparation
for a global scheduler.
chore(fmt): run go fmt
refactor(registry): Add GetAllMachines method to Registry
fix(machine): Allow BootId to be provided to Machine.New

The previous logic would always overwrite a Machine BootId with the
local value, even if it was provided to Machine.New. Now a client of
Machine.New can provide a specific BootId and it will be persisted.
feat(registry): Add AcquireLock method to Registry

The AcquireLock method allows a caller to attempt to acquire a lock
by providing a lock name, a context and a TTL. This will be reimplemented
once etcd provides this functionality natively.
feat(registry): Add ScheduleJob method to Registry

This method allows the caller to provide an unscheduled Job and have
it scheduled to a specific Machine.
feat(scheduler): Add a simple Scheduler

This scheduler will poll the Registry for unscheduled Jobs, attempt to
acquire a lock on one of those Jobs, then schedule it to a random
Machine.
feat(scheduler): Run a Scheduler in the coreinit binary
Merge pull request #8 from bcwaldon/global-schedule

Alpha Scheduler