added travis file

Adding a travis-ci file. I have a branch where I am using travis-ci to preform unit tests.

I did not include python 3 in this file because this project does not seem to support it.

https://travis-ci.org/michaelrice/pyvmomi/jobs/27107737
https://travis-ci.org/michaelrice/pyvmomi/jobs/27107738
Also seen here: 
https://jenkins.toastcoders.com/view/pyvmomi/job/python-pyvmomi-mine-tests-3.1.5/1/console

EDIT:
I think this also starts to add support to address issue #42