genie_python: controlling multiple instruments

As part of muon tuning, an instance of genie python is run inside Mantid on one computer and it needs to talk to MUONFE (read/set magnets) and HIFI/EMU/MUSR (begin/end runs). Currently the interaction with MUONFE is done with standard genie python cset/cget and separate locally written dcom based functions talk directly to ISISICP on HIFI/EMU/MUSR.

When muons move to ibex the current system will still work as ISISICP is still present, but it would be preferable if the DAE interaction was within genie_python. Currently begin() and cse() etc use the target specified in set_instruments, but in this case there are 4 machines that need to be interacted with in various way. What is the best way to deal with this use case in genie python? Is it possible to create a "musr" object based on "g" but with musr as the prefix, so then typing musr.begin() would be like g.begin() but with a different PV prefix?

## acceptance criteria

* approach for interacting/controlling multiple instruments from single genie python session determined