Add a health check

[goose-ws]

Adds a health check to ensure the container and the outside internet are reachable

[timrettop]

Any thoughts @binhex on accepting this PR?

[binhex]

hi, so health checking is already performed inside of the container via scripts, including ping checks, dns lookup, etc, so if for instance your internet connection dropped then the required processes would get restarted in the correct order, including new port assignment.

Looking at the healthcheck instruction in the docker docs this looks to be a more basic command to simply stop the container should any of the test fail, which IMHO isn't really what most users are after, most people simply want the container to retry connection until the user either fixes their internet connection or stops the container.

The other issue around dns lookups, there are times during initialisation of the container where dns lookups will correctly fail, this is due to strict iptable rules preventing ip leakage, which could in turn trigger the healthcheck and thus a incorrect exit of the container.