This fixes the remaining Python 3 syntax errors, so re-enable compileall
for contrib/ again.

(This is supposed to be temporary, until the code under contrib/ gets
cleaned up from all the remaining print statements.)

This syntax works on Python 2.6 through 3.x.  lib/ansible/module_utils
(and lib/ansible/modules) need to support Python 2.4, so I didn't touch
those.

'tox -e py26' would fail for me because python -m compileall would crawl
under .tox/py27 and, unsurprisingly, get SyntaxErrors on files from the
Python 2.7 standard library using syntax features not supported by
Python 2.6.

* Fix import pathing for units.mock
* Add some additional requirements
* Use compileall to test compatiblity with different python versions

(We have a jenkins build that creates a [testenv:jenkins] so it needs
there to be a default value

Purpose: so that devs can use tox to run v1 or v2 of ansible with various versions of python.
For example `tox -e py27-v2 will run python2.7 on v2. Currently, only py26 and py27 are run on v1 when
running just `tox` so that we aren't breaking builds.

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