Tests: Fix HLS Segmenter tests
Tests: Fix HLS Segmenter tests

These tests are pretty funky to reason through due to the way that timing
impacts them. For now, fix our start_ts to the start of a segment, so that we
can easily compute how many segments should be returned in each scenario.

pteich/StreamMachine,StreamMachine/StreamMachine,DreamNetwork/StreamMachine,pteich/StreamMachine,DreamNetwork/StreamMachine,cdgraff/StreamMachine,pedropapa/StreamMachine,StreamMachine/StreamMachine,pedropapa/StreamMachine,SCPR/StreamMachine,cdgraff/StreamMachine,SCPR/StreamMachine