Notifications can target robots, but the model did not reflect that

This fixes a breakage when deleting robots that have notifications targeting them.

data/database.py

@@ -1033,7 +1033,7 @@ class NotificationKind(BaseModel):
 class Notification(BaseModel):
   uuid = CharField(default=uuid_generator, index=True)
   kind = ForeignKeyField(NotificationKind)
-  target = QuayUserField(index=True)
+  target = QuayUserField(index=True, allows_robots=True)
   metadata_json = TextField(default='{}')
   created = DateTimeField(default=datetime.now, index=True)
   dismissed = BooleanField(default=False)

data/model/test/test_user.py

@@ -5,10 +5,13 @@ import pytest
 from mock import patch
 
 from data.database import EmailConfirmation, User, DeletedNamespace
+from data.model.organization import get_organization
+from data.model.notification import create_notification
+from data.model.team import create_team, add_user_to_team
 from data.model.user import create_user_noverify, validate_reset_code, get_active_users
 from data.model.user import mark_namespace_for_deletion, delete_namespace_via_marker
 from data.model.user import create_robot, lookup_robot, list_namespace_robots
-from data.model.user import InvalidRobotException
+from data.model.user import InvalidRobotException, delete_robot
 from util.timedeltastring import convert_to_timedelta
 from data.queue import WorkQueue
 from test.fixtures import *
@@ -117,3 +120,25 @@ def test_delete_namespace_via_marker(initialized_db):
 
   with pytest.raises(DeletedNamespace.DoesNotExist):
     DeletedNamespace.get(id=marker_id)
+
+
+def test_delete_robot(initialized_db):
+  # Create a robot account.
+  user = create_user_noverify('foobar', 'foo@example.com', email_required=False)
+  robot, _ = create_robot('foo', user)
+
+  # Add some notifications and other rows pointing to the robot.
+  create_notification('repo_push', robot)
+
+  team = create_team('someteam', get_organization('buynlarge'), 'member')
+  add_user_to_team(robot, team)
+
+  # Ensure the robot exists.
+  assert lookup_robot(robot.username).id == robot.id
+
+  # Delete the robot.
+  delete_robot(robot.username)
+
+  # Ensure it is gone.
+  with pytest.raises(InvalidRobotException):
+    lookup_robot(robot.username)