New read_routes6() function and unit tests

[guedou]

Here is an attempt at fixing Issue #109 by rewriting scapy.unix.read_routes6().

This patch provides mocked tests that ease reproducing outputs on several
operating systems. Scapy tests from regression.uts were also tested on real OS. I can not swear that this patch does not introduce any regressions or bugs by itself, but I tried my best not to.

read_routes6() can be tested as follows:

$ PYTHONPATH=. py.test test/mocked_functions.py -vx

It could be interesting to extend the idea mocked_functions.py to other part of
Scapy, and to run this tests with Travis along with the classic regression tests.

[p-l-]

As discussed IRL, @guedou can you check and tell me whether it would be possible to import mock from a standard .uts test file?

[guedou]

Here is an attempt to move the mocked tests to regressions.uts. The result is not a nice as the first attempt due to syntax limitations on UT Scapy.

Moreover, it introduces a dependency on the mock module, as it requires the mock module to be installed in order to pass all the tests. I wonder if we should move the mocked UT outside of regression.uts