clone to save space

https://blog.travis-ci.com/2017-06-21-trusty-updates-2017-Q2-launch
https://github.com/travis-ci/build-environment-updates/blob/master/2017Q2/gce/garnet-trusty/dpkg-manifest.diff

The configuration changes for the Discovery Service are now on the master branch of edx/configuration. There is no longer a need for a separate tag.

LEARNER-1375

This partially reverts commit 9b3b738a.

Further profiling showed that LMS/Studio startup times about tripled
when we dropped Docker Sync in favor of Docker's built in cached volume
mount system (going from 7-8s to anywhere betwen 22-28s). So we're
rolling back the part of that commit that removed Docker Sync and the
recommendations in the README.

However, we still want to keep the minimum version at 17.05 Edge, for
image building purposes. We also want to clarify that we did try using
Docker's built in cached volume support, so that people don't waste
time trying it again until Docker really implements "delegated" mode.

That shouldn't be there!

LEARNER-1375

The create_demo_data management command is now run for the E-Commerce Service. This creates a verified seat for the demo course, allowing developers to get started testing payments with minimal effort.

LEARNER-1375

This will help get developers up and running with payments.

LEARNER-1375

We don't have a simple way of managing groups at the moment. This is the next best alternative as managing groups/permissions is a bit beyond the scope of the current task.

LEARNER-1375

- Remove sync provisioning to force upgrade.
- Add 17.05 as minimum version

See https://docs.docker.com/docker-for-mac/osxfs-caching/ for details.