Jackie Harbaugh, mother of new Giants coach John Harbaugh as well as Chargers coach Jim Harbaugh, takes a timeout from the House of Harbaugh for some Mother’s Day Q&A with Post columnist Steve Serby. Q: Your husband Jack tells a tale that your face touched the mashed potatoes when John revealed he would like to pursue coaching.  A: Well, it just depends if you want Jack’s story, which makes everybody laugh, or you want the truth.  Q: (Laugh) Let’s go with the truth.  A: (Laugh) John had