Added UserData Test to Instance Test Suite

Added UserData test to instancetest.py.  The purpose of this test is to confirms if the userdata service is working correctly.  Files tests are based upon the [file formats accepted by Cloud-Init](http://cloudinit.readthedocs.org/en/latest/topics/format.html).  Test compares contents of a file (--user-data-file option) or string (--user-data option).