Complete the function normalize_test that takes the testing set X_test and the training set means and standard deviations and returns a normalized feature matrix. Each column should subtract the mean of the corresponding column from X_train and divide by the standard deviation of the corresponding column from X-train. For example, each element in the first column of X_test should subtract the mean of the first column of X_train and divide by the standard deviation of the first column of X_train.