Investigate why remote_monitor takes time to shutdown after experiment is over #35

I've observed this in long experiments with large query lookback periods. There are long multiple instances of:
ssh -o StrictHostKeyChecking=no milindsr@node0.scratch1.cloudmigration-PG0.utah.cloudlab.us "pgrep -f remote_monitor.py" Remote monitor is still running. Will check again in 10 seconds

Not a problem wrt functionality but figuring this out will speed up running of experiments.
My hypothesis was that this was because of remote_monitor and/or PrometheusClient dumping large files and taking time to do so.
However, remote_monitor's monitor_output.json is small and PrometheusClient has been updated to stream results to file instead of dumping them all at once after the end of an experiment.