IGearClient.add accepts environment variables - fixes 568

Fixes #568 
Maybe this should just be a dictionary. And the gear environment ID can be fixed to match the name of the unit. gear allows the concept of shared environments, but I don't think we'll need that ...at least not yet.

See "Set and retrieve environment files for sharing between containers (patch and pull operations)" in  https://github.com/openshift/geard/blob/master/README.md