add detection of launch-time env and optional propagation to run-time

[afmcc]

suggestion : currently tardis has a configured default run-time environment for jobs, and will include activation of that environment as part of the run*.sh wrapper(s) it generates. This can be tweaked using the -shell-include-file argument. These run time environments do not need to be available on the node on which you are running tardis - they are only needed at run-time, not launch-time; however in some situations, it would be convenient for tardis to detect any activated environment at launch time, and include activation of that environment in its run-time scripts. (This behaviour could be controlled by one or more configuration options such as use_active_conda_environment - sometimes you might not want it to do this). Note that the -shell-include-file arg may be supplied to accomplish other things than setting up env - so even if an env is detected and used , any -shell-include-file request should still be honoured (which is not the current behaviour, which is a bug).