requirements_common.txt: Upgrade iptools==0.6.1 for Python 3 and ipv4/ipv6

[cclauss]

https://pypi.org/project/iptools v0.4.0 is currently failing our build process on Python 3 because of a syntax error. This PR upgrades to a Python 3 compatible release that also supports the distinction between ipv4 and ipv6

[mekarpeles]

Seeing issues with:

Traceback (most recent call last):
  File "/opt/openlibrary/deploys/openlibrary/openlibrary/infogami/utils/template.py", line 146, in saferender
    result = t(*a, **kw)
  File "/opt/openlibrary/venv/local/lib/python2.7/site-packages/web/template.py", line 868, in __call__
    return BaseTemplate.__call__(self, *a, **kw)
  File "/opt/openlibrary/venv/local/lib/python2.7/site-packages/web/template.py", line 781, in __call__
    return self._join_output(out)
  File "/opt/openlibrary/venv/local/lib/python2.7/site-packages/web/template.py", line 787, in _join_output
    for name, value in out:
  File "/opt/openlibrary/deploys/openlibrary/openlibrary/openlibrary/templates/type/author/view.html", line 59, in __template__
    $ library = (get_library() if 'inlibrary' in ctx.features else None)
  File "/opt/openlibrary/deploys/openlibrary/openlibrary/openlibrary/core/inlibrary.py", line 106, in get_library
    lib = d_ip.get(web.ctx.ip)

[cclauss]

Should I revert? What is the actual Exception being raised?