Evaluate runtime environment definitions in Common Workflow Language (CWL)

[nuest]

See presentation 2017-03-17 CWL @ HTS-CSRS "BioCompute Object" Workshop at https://docs.google.com/presentation/d/1a-iQYhu52F5L0-UaD-5mGCpWIJCxdVEH9a1i4Rx8BOA/edit#slide=id.g15b9625092_0_337

CWL also defines runtimes, so there is probably something to learn from that: http://www.commonwl.org/draft-3/CommandLineTool.html#Runtime_environment