Task #8888: Added open() and close() to RPC class to hide implementation details of __enter__ and __exit__

Task #8888: Do not require $LOFARROOT/bin for lofarinit.sh to work (happens when installing a python lib)

Task #8899: Moved python coverage check to separate bash function, and added lib to store database credentials for python services.

Task #8888: added OTDBBusListener which is a concrete implementation of the BusListener, listening to otdb status events and calling on<SomeEvent> methods

Task #8888: Service is a frombus listener, so inherit from new class AbstractBusListener -> refactored out duplicate code

Task #8888: added abstract class AbstractBusListener to listen on a bus, and let the user implement one simple handle_message method

Task #8746 Adding a error_tolerance option to the executable_args master script. This controls if the step exits at the first error or if a pipeline should continue with the successfull processed steps. Usage in the parset on a step by step basis: stepname.control.error_tolerance=<Bool>

Task #8899: Allow broker options to be specified in FromBus/ToBus constructor (final final fix for tests without auto-reconnect, hopefully)