NFD

The NFD integration tests have somewhat fallen by the wayside over the past year or two. This is likely at least partially due to the heavyweight requirements to run them (4x VirtualBox VMs, each with 6GB of RAM and 4 cores). Therefore, we should add support for a lighter-weight platform to run the integration tests on, such as Docker. This would also ease adding integration testing to Jenkins builds of submitted patches, which would improve the testing of NFD and improve awareness of newly-breaking integration tests, improving their value.

As part of this, the platform should be updated from Ubuntu 16.04 to Ubuntu 18.04, as the former will enter EOL soon and is no longer an officially supported platform of NFD.