fix(schedule-all): Stop rescheduling all-machine jobs

Jobs started with --all-machines were being rescheduled to
other machines on EventMachineDeleted. This behavior was not
correct. Stop it.
fix(schedule-all): reschedule to machine after it comes back

If a job was scheduled with --all-machines, a machine could die, lose its job,
and come back up without having the job rescheduled to it. This commit removes
the dead machine from the schedule so it can be rescheduled by the JobWatcher
when the machine comes back up.
refactor(engine): Use constant for ScheduleAllMachines functionality
Merge pull request #33 from bcwaldon/schedule-all

Fix two nasty --all-machines scheduling bugs