Add python 3 to Travis-CI build matrix

This adds Python 3.2 to the list of Python versions to use for the
Travis-CI test builds of NIPAP.
Force use of Python 2.x for nipapd

nipapd is known to not be Python 3 compliant, so we force the use of
Python 2. This should still allow us to run it under the Python 3 job of
Travis-CI so that other components (that rely on nipapd) can be tested
using Python 3 while nipapd is still running using Python 2.
authlib: convert exception handling to Py3 style
daemon: convert exception handling to Py3 style
authlib: convert exception handling to Py3 style
backend: convert exception handling to Py3 style
xmlrpc: convert exception handling to Py3 style
Merge pull request #596 from plajjan/travis-ci/add-python3

Add Python3 test to Travis-CI build matrix