Add automated tests for background refresh
Our CI tests don't currently include a test that backgrounds are being reloaded. I've done one manually with the following parameters:
--cohfar-assignfar-silent-time 0
--finalsink-snapshot-interval 1800
--cohfar-accumbackground-snapshot-interval 90
--cohfar-assignfar-refresh-interval 250
--cohfar-assignfar-refresh-offset 100
--cuda-postcoh-detrsp-refresh-interval 300
--cuda-postcoh-detrsp-refresh-offset 100
and running that without pregenerated backgrounds. Then I checked that the 'nevent_1' column updated multiple times in its first zerolag dump.
It's an OK test, but it doesn't actually cover detrspmap refresh. I'm unsure of an output that would correspond to that being updated, we may need to simply add a log each time postcoh_utils.c/cuda_postcoh_map_from_xml
is called. But I think it's a bad pattern to add logs corresponding to integration tests.