Adds the ipaddress compat library backport from Python 3.x (ansible#4…

…2265)

This library is a backport (to 2.x versions of Python) of the code
that is found in the mainline versions of Python 3.x. It is being
included so that networking vendors, and others, can make use of it
without needing to add a python module dependency to their own modules.

A separate dependency would add to user burden of satisfying those
dependencies before using some Ansible modules.

In a previous core meeting, this was approved. Naming of the directory
it is found in was up for debate, but "compat" was the first directory
to have some sort of concensus.