Start shouldn't require local unit file

[stongo]

Forcing the use of fleetctl submit unitFile and fleetctl start unit for the start method is too limiting for my use. For my use case I need to be able to stop/start units without submitting a new unit file.
Would you be cool with a PR to add an option to bypass the submit step?

[lukebond]

hey @stongo good idea. i guess it was written on the assumption you wanted to submit and start a unit.

i guess you'd want something that would ultimately just end up calling fleetctl start unit-name and not providing the whole unit file yeah?

[stongo]

@lukebond that's exactly it, just want to execute fleetctl start unit-name
working on a PR for this now :)