Clean up the way suite environment variables get to the job script.

 * handle static and task-host-specific variables separately
 * pass the environment dicts directly to jobfile module
Same for the submit command.
Merge branch 'master' into suite-env-housekeeping
Fix previous merge.
Merge branch 'master' into suite-env-housekeeping
Merge pull request #409 from hjoliver/suite-env-housekeeping

Clean up the way suite environment variables get to the job script.