* Sort packages to install.
* Add python-argparse to centos6 docker image.
* Add gcc and python dev lib to docker images.
* Add python cryptography to docker images.
* Add coverage using pip instead of OS packages.
* Update old pip versions in docker images.
* Exclude */pyshared/* from coverage reporting.
Add tox integration to run unittests in supported python releases.
Travis-CI is used for test execution.
Additionally, the unittest TestQuotePgIdentifier was updated to support
using assert_raises_regexp on python-2.6.
Sample travis-ci output available at
https://travis-ci.org/ansible/ansible/builds/54189977