Custom userdata tests

Added userdatatest.py to help test cloud-init with particular images.  Added additional files to user-data-tests for templates that can be used for testing.  Files tests are based upon the [file formats accepted by Cloud-Init](http://cloudinit.readthedocs.org/en/latest/topics/format.html), which are supported in [Amazon Linux images](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/AmazonLinuxAMIBasics.html#CloudInit).  Test compares contents of a file (--user-data-file option) or string (--user-data option).