Change BEAMLINE_PREFIX value

Changed the default BEAMLINE_PREFIX value to something that won't
conflict with any actual beamline
Change how the live listener algorithm is started

Start the live listener algorithm with the option to reuse the existing
workspace (instead of creating a new one and saving the old one at
every run transition).  Also add some code to the start_live_listener
function to make sure that the MonitorLiveData algorithm is actually up
and running before returning from the function.  (It looks like we had a
case where we returned from start_live_listener before MonitorLiveData
was running, the watchdog loop caught that and tried to execute
start_live_data again.  That didn't work so well...)