Send info about ability to use secure env vars to worker

This commit sends info on availbility of secure env vars to worker.
Additionaly it allows to use secure env vars in pull requests as long as
the commit was pushed to the same repository.
Use simple states from rubygems
Merge pull request #217 from travis-ci/ps-secure-env-vars-in-prs

Send info about ability to use secure env vars to worker