SP-1857 Emu-Recv Testing Fixes

During manual testing of the visibility receive workflow with the latest emu-recv I've noticed problems in following situations:

• Stack dump when the emu-recv config file is not found only describes that the datamodel is empty
• Using a datamodel measurement set containing only a single timestep causes an out of bounds exception
• kubernetes volumes mounts can't already exist on the docker image, a custom plasma socket needs to be supported rather than /tmp/plasma

To address the problems the following has been changed:

• Changed default emu-recv config to an empty config and raise exception if a config is specified that does not exist
• Add a utility function for calculating baselines in a measurement set that works for both single-timestep and multi-timestep measurement sets
• Pass the plasma socket through to the mswriter functions