fix(controller): destroy app containers in parallel

When we call app.destroy(), each container is destroyed in series. Since
we now rely on Fleet's state to respond, we are getting a more accurate
idea of what state the container is actually in. Because of this,
c.destroy() was taking a very long time waiting for a response from
fleet. iThis wasn't a problem before because we were waiting for
django-fsm, which basically said "yup, I told fleet to destroy the
container. It's dead now", which wasn't entirely true.

Switching to destroying containers in parallel makes this operation much
faster.

Author: Matthew Fisher

controller/api/models.py

@@ -181,8 +181,11 @@ def create(self, *args, **kwargs):
 
     def delete(self, *args, **kwargs):
         """Delete this application including all containers"""
-        for c in self.container_set.exclude(type='run'):
-            c.destroy()
+        try:
+            # attempt to remove containers from the scheduler
+            self._destroy_containers([c for c in self.container_set.exclude(type='run')])
+        except RuntimeError:
+            pass
         self._clean_app_logs()
         return super(App, self).delete(*args, **kwargs)