fix: allow stopping services in "starting" state

[IronCore864]

Pebble has a 1-second okayWait time period for starting services, after which, if the service is still not exited, it's considered as "running". Previously, when services were still in the starting state within this 1-second okayWait period, they couldn't be stopped. This causes some issues in tests. And, just because services have just started doesn't mean they shouldn't be allowed to stop. This PR allows services in the starting state (within the 1s okayWait period) to be stopped, no matter if it's the daemon exits (Ctrl+C in the console) or the pebble stop command is issued.

Fixes #410
Fixes #502

Also adding two test cases:

1. servstate: use a mock service which sleeps a while then create a side effect, stop the service immediately after it's started, and the side effect won't be created.
2. daemon: start a service, stop the daemon before the okay delay, and a stop change should be created. Whether the service is actually terminated or not isn't tested because it's tested above in the servstate.

[benhoyt]

I'm good with the fix, thanks. However, I wonder if we can spend some time on test cases. Ideally we could have a test for each of the issues this will close:

• If a service is stopped during okayWait, it 1) returns the "stopped before the okay delay" error, and 2) is actually terminated
• If the daemon is stopped during okayWait, the service is terminated