[Reviewer: Alex] UTs run much faster if we don't pause for 1s every time we destroy a Sig...

...nalHandler

More fixes addressing https://github.com/Metaswitch/sprout/issues/588. This brings it down from 24s to 10s, and I have another change in Sprout bringing it down to 6s.

Tested by running the UTs, but not live - I don't think that's worthwhile as we only destroy the updaters on program termination.
Hmm. It doesn't feel like the Updater should own the signal handler (and therefore shouldn't be cancelling it). Can you do this from `main()` instead?