Automate the addition of dns-records to hosts file

[febbraro]

Outrigger DNS has a number of cases where it will not work:

• DNS resolution is not supported on Windows
• DNS resolution is not supported on MacOS when offline (on the airplane, say)
• Local networking is in some kind of temporary error state.

As a workaround for these issues, we'd like to support easy management of the local hosts file.

rig dns-records --install (or perhaps --save) should inject the output of that command to /etc/hosts and the Windows equivalent.

HELP WANTED
This issue is a great opportunity to learn Golang, the contribution workflow of rig, and incidentally improve rig!

Notes

• Given the hosts entries will go stale as containers are removed and started, these entries cannot be permanent. Should there also be a cleanup command? Should rig stop run it?
• How will this interact with VPNs?
• Users guided to use this command will need guidance about what's happening and how to review it, seems like we'll need some INFO logging to explain.

Testing

• Use docker-compose run --rm lint to apply the full suite of static analysis tools. If there is a failure, you aren't done yet!
• Use docker-compose run --rm compile to confirm your code compiles.
• You can use the binary resulting from the compilation step (located in ./build/darwin/rig) to test that you can install records and then see how curl/browser finds your containers. You can quickly spin up a container to test with docker run --rm -l com.dnsdock.image=outrigger -l com.dnsdock.name=test outrigger/apache-php:php70

[febbraro]

Possibly just add a "--save" or "--remove" to the command to help manage it?

[grayside]

EDIT: Rolled up the relevant parts of this comment into a summary rewrite for new contributors.

[dnmurray]

unix only, so far: #172