automatically upload all passing builds to s3

Automatically uploads all passing builds of master to s3 for developer
convenience.

To add needed environment variables .travis.yml

gem install travis
travis encrypt S3_ACCESS_KEY_ID=yourkey --add
travis encrypt S3_SECRET_ACCESS_KEY=yourkey --add
Merge pull request #2433 from fivetanley/auto-upload-passing-builds-to-s3

automatically upload all passing builds to s3