use log.debug (not log.exception) upon exception in IMS.stop_instrument_agent_instance in base test class' _stop_instrument: the expected situation when this happens is when the instrument has already been  terminated by its parent platform, so printing the stacktrace is unnecessary noise in the logs.
merge upstream/master
Merge pull request #1287 from carueda/master

log.debug instead of log.exception - failure to stop instr agent is expected when the parent platfrom has already taken care of that