Add ElasticSearch service

[kostajh]

• Install Docker in VM creation
• Run ElasticSearch as a container using the image from releng/dev-images which has WMF plugins
• Run CirrusSearch setup scripts in postinstall.sh

Periodically cleaning up old search index data is not done in this patch. It can be done by deleting the volume associated with the container (since this is considered throwaway data).

It would be nice if runJobs.php ran periodically for the wiki, as that's needed to process updates to the search index. Ideas welcome on how to do that.

Fixes #356

[kostajh]

warning; untested code.

[MatmaRex]

Sorry I haven't responded yet, I will have a look eventually.

I'm mostly wondering how this will interact with the deduplication of the source code that patchdemo has. I don't know enough about Docker to guess what will happen.