Use 'env' log level by default
This is problematic. It's basically saying 'if
MU_LOG_LEVELis not defined set
--log-level=env'. But then Zebu will check
MU_LOG_LEVELwhich is not defined, right?
Oh woops, stupid me, you should just delete the line entirely, and let zebu handle determining what the log level should be. (Which by default is 'env' (which will be stored in boot images) and when vm's are created/resumed it will use MU_LOG_LEVEL if set, otherwise None).