Added UserData Test to Instance Test Suite Refactored

Added UserData test to instancetest.py.  The purpose of this test is to confirms if the userdata service is working correctly, and tests to make sure userdata of [16K size is accepted, per AWS spec](http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/AESDG-chapter-instancedata.html).  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).  

Added userdatatest.py to help test cloud-init with particular images.  

Added directory user-data-tests for templates that can be used for testing.