Made connection errors more user-friendly (#57)

src/Microsoft.SqlTools.ServiceLayer/Connection/ConnectionService.cs

@@ -162,8 +162,16 @@ namespace Microsoft.SqlTools.ServiceLayer.Connection
                 connectionInfo.SqlConnection = connectionInfo.Factory.CreateSqlConnection(connectionString);
                 connectionInfo.SqlConnection.Open();
             }
-            catch(Exception ex)
+            catch (SqlException ex)
             {
+                response.ErrorNumber = ex.Number;
+                response.ErrorMessage = ex.Message;
+                response.Messages = ex.ToString();
+                return response;
+            }
+            catch (Exception ex)
+            {
+                response.ErrorMessage = ex.Message;
                 response.Messages = ex.ToString();
                 return response;
             }

src/Microsoft.SqlTools.ServiceLayer/Connection/Contracts/ConnectResponse.cs

@@ -16,10 +16,20 @@ namespace Microsoft.SqlTools.ServiceLayer.Connection.Contracts
         public string ConnectionId { get; set; }
 
         /// <summary>
-        /// Gets or sets any connection error messages
+        /// Gets or sets any detailed connection error messages.
         /// </summary>
         public string Messages { get; set; }
 
+        /// <summary>
+        /// Error message returned from the engine for a connection failure reason, if any.
+        /// </summary>
+        public string ErrorMessage { get; set; }
+
+        /// <summary>
+        /// Error number returned from the engine for connection failure reason, if any.
+        /// </summary>
+        public int ErrorNumber { get; set; }
+
         /// <summary>
         /// Information about the connected server.
         /// </summary>