Bootstrapping a VSTS Linux build agent for Docker containers

1. Create an Ubuntu 17.04 VM in Azure
2. Install dotnetcore using the instructions here.
3. Install the Docker apt-get package using the instructions here.
4. Download and run the VSTS agent Docker image and run it as a Docker container itself using the instructions here, e.g. sudo docker run -e VSTS_ACCOUNT=myvstsaccountname -e VSTS_TOKEN=abcdtokenherefromportal -e VSTS_POOL="Docker Build Agents" -e VSTS_AGENT="myagentname" -it -v /var/run/docker.sock:/var/run/docker.sock microsoft/vsts-agent