Clean up Travis scripts and config

* Some spacing to make things more readable.

* Move a random export that was somehow in .travis.yml into .travis.sh,
  where the rest of them are.
[release] only push the release tag

Do not push all tags, just the one we merged to relese.
Merge pull request #101 from spotify/rohan/travis

Clean up Travis scripts and config
HeliosClient should return JobDeleteResponse, not null, when deleting nonexistent job

Currently if you try to delete a nonexistent job, HeliosClient returns null,
so the caller doesn't know what happened. This caused a NPE in TemporaryJobs,
because it tried to delete a nonexistent job, and didn't expect the client to
return null. It now returns JobDeleteResponse with the status set to
JOB_NOT_FOUND so the caller can decide if this should be handled as an error
or not.
Merge pull request #102 from spotify/drewc/push-only-new-tag

[release] only push the release tag
Merge pull request #103 from spotify/rculbertson/job-delete-response

HeliosClient should not return null, when deleting nonexistent job
We don’t need the release branch anymore

and it causes problems with Jenkins and git because git gets into a detached state