[AIRFLOW-1186] Sort dag.get_task_instances by execution_date

task.get_task_instances is sorted by
execution_date, so we sort
dag.get_task_instances by execution_date so it
doesn't break
duration chart

Closes apache#2284 from OpringaoDoTurno/fix-duration

airflow/models.py

@@ -3079,7 +3079,7 @@ def get_task_instances(
         )
         if state:
             tis = tis.filter(TI.state == state)
-        tis = tis.all()
+        tis = tis.order_by(TI.execution_date).all()
         return tis
 
     @property
@@ -3887,7 +3887,7 @@ def set_dirty(dag_id, session=None):
         """
         :param dag_id: the dag_id to mark dirty
         :param session: database session
-        :return: 
+        :return:
         """
         DagStat.create(dag_id=dag_id, session=session)
 
@@ -3964,11 +3964,11 @@ def update(dag_ids=None, dirty_only=True, session=None):
     @provide_session
     def create(dag_id, session=None):
         """
-        Creates the missing states the stats table for the dag specified 
-        
+        Creates the missing states the stats table for the dag specified
+
         :param dag_id: dag id of the dag to create stats for
         :param session: database session
-        :return: 
+        :return:
         """
         # unfortunately sqlalchemy does not know upsert
         qry = session.query(DagStat).filter(DagStat.dag_id == dag_id).all()
@@ -4078,7 +4078,7 @@ def find(dag_id=None, run_id=None, execution_date=None,
         :type state: State
         :param external_trigger: whether this dag run is externally triggered
         :type external_trigger: bool
-        :param no_backfills: return no backfills (True), return all (False). 
+        :param no_backfills: return no backfills (True), return all (False).
         Defaults to False
         :type no_backfills: bool
         :param session: database session