Fix ifconfig parse logic failing on some tunnels

[Woellchen]

Tunnel interfaces that have a line similar to
"tunnel inet 192.0.2.1 --> 192.0.2.2" would fail the network resolver
because IPs were extracted through two separate IP + mask patterns.
However, in the example above, there is no such thing as a netmask.

This fix merges the patterns and extracts the IPs and netmasks
together so that no mismatches can occur. It might also fix some
cases where only the netmask would be nil and therefore produce an
invalid binding that could in turn resolve to the wrong (outer) IP of
the tunnel instead of the inner IP.

[puppetlabs-jenkins]

Can one of the admins verify this patch?

[joshcooper]

Thanks @Woellchen! In the first commit that demonstrates the failure, can you mark the failing test(s) as pending? And then remove the pending in the second commit. This is important so that each commit passes if we later need to git bisect.

Or you can keep the commits as-is and I can squash them when merging. Let me know which sounds better.

[Woellchen]

Hey @joshcooper, thanks for getting back to me!
I see your point and I have marked the tests as pending in the first commit, and unmarked them in the following one.
Please check one more time if this looks good to you now :)

[joshcooper]

Closing and reopening to trigger the right set of checks

[Woellchen]

Hey @joshcooper! To avoid further confusion and delays I have just merged the two commits into one and skipped the failing tests commit that was meant to demonstrate the failure. I have also rebased the branch once again. I hope that this way we can conclude this PR for good :)