[RTA/DPA BW tests]: Compress log files
Sharing the functionality added in !312 (merged) in BandwidthTestHandler. I tried to follow the convention already in place, but happy to move things around in a different way if preferred.
In a local test I observe ~20x reduction in file size: 72 MB to 4 MB on a log from a HLT2+Sprucing bandwidth test that I ran the other day.