Adrianne Haslet -- FINISHES BOSTON MARATHON ... 3 Years After Losing Leg In Bombing

5:21 PM PT -- Adrianne just got a shout out from President Obama ... who wrote:  "Thank you, Adrianne, for being Boston Strong. Terror and bombs can't beat us. We carry on. We finish the race!"  SHE DID IT!!!  Adrianne Haslet has just…