Trigger a Travis test build on PRs / Commits

Adds support for Travis, runs tests on PR / commits. Currently only testing Python 2.7 as we have a few problems with Python 3 (#131 fixes a big problem there). Excluded Python 2.6 intentionally (see #125)

In Travis a test is ran inside a virtualenv that does not pull in global side packages so I had to make a very nasty hack to copy `libxml2`, `libvirt` and `guestfs` python bindings into the container.  None of those are installable via pip which causes some headache. I am pulling in m2crypto via pip with a specific sslv2 fix that the distro packages have fixed but upstream hasn't, not my favourite approach but reduces the need to do the copy over hack.

I am making Travis run each test directory as it's own "suite" to get parallel testing going and faster results.

An example of a passing build: https://travis-ci.org/helgi/oz/builds/13278492

Additionally using coveralls.io for code coverage reporting. To get the coverage reported then this repo needs to be enabled on coveralls.io - Currently coveralls.io doesn't seem to like combining the results correctly for the overall run since each test "suite" is being ran in parallel, I have a ticket open about that at https://github.com/lemurheavy/coveralls-public/issues/156

If it is ran as a single longer build then the main coverage report shows up properly

The `/bin/true` to `/bin/ls` was a change to appease the ozutil test run on OS X