Created by: bardiharborow
Resolves #17163 (closed). Ubuntu Trusty containers are now available on Travis, removing the last obstacle stopping us moving to the container based environment. This cuts build times by about 15 seconds.
Regarding the other changes: Ruby 2.3.1 comes preinstalled on the new images, so I have removed the install directive. The npm install directive has been made conditional as only the Node 4.x environment will have npm 2.x. --retry=3 has been added to the bundler command to bring it in line with Travis' default and to provide greater network stability. NPM_CONFIG_PROGRESS="false" has been removed as npm/npm#11283 seems to be fixed. Git --depth has been lowered.
Coming soon in another PR, is switching to using the Travis apt addon to download the Google Cloud SDK (blocked on travis-ci/apt-package-whitelist#3515) and switching to using the Travis sauce_connect addon rather than using grunt-saucelabs (blocked on further investigation).