Network pre-flights: Detect network issues and present actionable feedback

[tstromberg]

Many incoming issues are due to local network access problems, mostly from proxies, but many also due to HyperV:

failed/local-networking startup failures due to networking issues

We should have a basic connectivity check to the minikube VM, in a way that detects problems in a user-friendly way, such as:

* Unable to establish a network connection to the VM: please check http://x
  for possible solutions.

And at least until we have good story around offline usage:

* Unable to establish a fully functional internet connection: please check http://x 
  for possible solutions.

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[tstromberg]

Problems to warn about:

• HTTP client to internet
• HTTPS client to internet (storage.googleapis.com) - HTTPS is important due to interception issues!
• HTTP client to VM (such as apiserver)
• DNS client from VM to internet
• HTTP client from VM to internet

These failures should point to a connectivity problems document where users can read up on solutions.