The remsim_client code already used FSMs for the connections
to both remsim-server and remsim-bankd. However the 'main' part of the
program was not yet implemented as a FSM, making it somewhat difficult
to perform the right actions in every possible situation.
This commit re-structures the code around a central main_fsm, which
gets notified from the per-connection FSMs and which handles the common
processing. It also handles the execution of external script commands,
and hence further unifies the code base between the different backends
(simtrace2, ifd_handler, shell)
Closes: #4414
Change-Id: I44a430bc5674dea00ed72a0b28729ac8bcb4e022
