CM changes to termination and panic.
* For termination, added a flag to the slice that marks it for termination. DeleteSlice sets this if the slice is "busy" (start,restart,reload) and the "cancel" flag is provided. We also mark the underlying experiment as canceled, to stop ossetup and osload early. We then wait for "busy" to clear, and then kill the slice. The new termination flag in the slice is used by the expire daemon, in case our wait loop dies early (say, boss reboot), we can catch the the termination there instead. * Panic gets essentially the same changes as termination, except of course instead of terminating, we put the underlying experiment into panic mode. Note that we still need to be able to lock the slice to do either termination or panic, and so the caller has to be able to deal with retrying if they get back a busy response. In general, we do not lock slices for very long except during reload and restart, I am still working on dropping the lock during those (like we already do for Start). Disk imaging is another place we currently need to wait for, that needs to be worked on as well.
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