1) Do not fail in case a bind address cannot be obtained

If netutil.ChooseBindAddress() fails looking up IP route tables
it will fail with an error in which case the kubeadm config
code will hard stop.

This scenario is possible if the Linux user intentionally disables
the WiFi from the distribution settings. In such a case the distro
could empty files such files as /proc/net/route and ChooseBindAddress()
will return an error.

For improved offline support, don't error on such scenarios but instead
show a warning. This is done by using the NoRoutesError type.
Also default the address to 0.0.0.0.

While doing that, prevent some commands like `init`, `join` and also
phases like `controlplane` and `certs` from using such an invalid
address.

Add unit tests for the new function for address verification.

2) Fallback to local client version

If there is no internet, label versions fail and this breaks
air-gapped setups unless the users pass an explicit version.

To work around that:
- Remain using 'release/stable-x.xx' as the default version.
- On timeout or any error different from status 404 return error
- On status 404 fallback to using the version of the client via
kubeadmVersion()

Add unit tests for kubeadmVersion().
Co-authored-by: Alexander Kanevskiy <alexander.kanevskiy@intel.com>