(QENG-1126) Help FOSS testing flexibility in Beaker-Rspec

Add logic to allow for IS_PE='no' or 'false' to mean FOSS testing, defaults to nil which means PE, only way to do this outside of host config in Beaker-Rspec
Unfortunately yes as we assume if nothing is set we are PE but operate differently on merge when ENV is set or not.  If it is set it will override the config file.  The environment variables are used as an override to instead and have higher merge priority than configs.  We can not assume if it is not set we are always PE, if we are testing a config that is explicitly type: foss it will be overridden if we set it to PE.