TOP-1158 multiple scan integration test

This adds the multiple scan integration test, based on an existing draft MR to the pipeline. Work has been done to produce a new graph, that shows the average of all channels plotted over time ("epoch_offset").

It also adds a way to explicitly start and stop output capturing -- this was added to allow capturing of multiple scans to a single PCAP file. Currently, if captures are not started explicitly, the original behaviour where a file per scan is captured still remains. The file name for multiple scans are different from those that are captured individually. One item that needs future work is the case where multiple explicit capture start and stops are done. Currently the later scans will overwrite files for the previous scans, as the timestamp that forms part of file name is unique per test case, rather than unique per file.