Test driver improvements (#117)

* Refactored the test driver to work with xunit in addition to the command line

* Fix behavior of property

src/Microsoft.SqlTools.ServiceLayer/QueryExecution/Contracts/ResultMessage.cs

@@ -40,5 +40,12 @@ namespace Microsoft.SqlTools.ServiceLayer.QueryExecution.Contracts
             Time = DateTime.Now.ToString("o");
             Message = message;
         }
+
+        /// <summary>
+        /// Default constructor, used for deserializing JSON RPC only
+        /// </summary>
+        public ResultMessage()
+        {
+        }
     }
 }