Service.start should take a callback

[Jaymon]

Currently, in some code I do something like this:

Upstart("SERVICE_NAME", False).start()

logger.debug("SERVICE is starting")

c = Client()
for x in range(10):
    r = c.get("/some/url")
    if r.code == 204:
        break
    else:
        logger.debug("SERVICE has not started")
        time.sleep(0.25)

logger.debug("SERVICE is ready")

It would be great if I could put just the meat into a callback and then the actual .start method will handle the looping and checking the return value of the callback.

This should be implemented in one of two ways, .start should take a check callback, and the service should have a .check method that returns True, so subclasses could override the .check method, or if they pass it in then it will be set to self.check.