ES instance for test builds

We're using a docker instance to setup ES server for every GitLab EE build. Since ES 5.0 it became memory hungry and we keep seeing "Cannot allocate memory".

I propose to set up our own ES server somewhere in GitLab infrastructure and use it instead of docker. That would save us lots of memory and we would never see these "Cannot allocate memory" errors anymore.

The index name could be chosen based on BUILD_ID.

/cc @smcgivern @ayufan @nick.thomas @pcarranza