os.LookupEnv() was not available yet at the time this was
implemented, but now provides the functionality we need,
so replacing our custom handling.
Signed-off-by: Sebastiaan van Stijn <github@gone.nl>
… or could be in `opts` package. Having `runconfig/opts` and `opts`
doesn't really make sense and make it difficult to know where to put
some code.
Signed-off-by: Vincent Demeester <vincent@sbr.pm>