Fix bug where testing profile connection info was being ignored

This fixes a bug where if using a testing profile, TempJobs would
attempt to connect to DOCKER_HOST instead of the domain or endpoint
specified in the profile.

Also added comments to the create() method to make the logic more
clear.
Merge pull request #239 from spotify/rculbertson/temp-job-create-fix

Fix bug where testing profile connection info was being ignored