add travis.yml

@jzoldak @benpatterson @cgoldberg 


See this PR for test results: https://github.com/clytwynec/harprofiler/pull/1
you shouldn't need to start xvfb, or fiddle with display variables.

harprofiler has xvfb starting/stopping built in via use of the PyVirtualDisplay module (a requirement).
it is controlled in the config.yaml file... enabled by default with:
virtual_display: true

I was able to run in an ssh'ed server env (similar to a build slave) fine.
Can you try without the before_install step removed and see if it still works ok?

if for some reason this doesn't work on the travis worker, we need to configure things so we don't start xvfb twice.