'net' module: tests and fixes

So far this updates #308 with a very basic test suite, and fixes IPv4 and/or IPv6 address detection.
I get a "not ok" for that test which then stops the other tests from running:

```
    ok 103 equal
    ok 104 ok
    ok 105 ok
    not ok 106 test/suite/net.js
      ---
        exit:    8
        command: "/Users/jialiya/projects/technical/workspace/test/nate-firmware/firmware/deps/runtime/out/Release/colony net.js"
      ...

    1..106
    # tests 106
    # pass  105
    # fail  1
```

Weirdly enough I also get 112 tests when running through ttt instead of tinytap.