push notifications: Fix very minor quirk when adding tokens.

When we push a device token, we want to clean out any other user's
tokens on the device, but not the current user's.  We were wiping
away our own token, if it existed, before creating it again.  This
was probably never a user-facing problem; it just made for dead code
and a little unnecessary DB churn.  By excluding the current user
from the delete() call, we exercise the update path in our tests now,
so we have 100% coverage.

zerver/views/push_notifications.py

@@ -19,13 +19,14 @@ def add_push_device_token(request, user_profile, token_str, kind, ios_app_id=Non
 
     # If another user was previously logged in on the same device and didn't
     # properly log out, the token will still be registered to the wrong account
-    PushDeviceToken.objects.filter(token=token_str).delete()
+    PushDeviceToken.objects.filter(token=token_str).exclude(user=user_profile).delete()
 
     # Overwrite with the latest value
     token, created = PushDeviceToken.objects.get_or_create(user=user_profile,
                                                            token=token_str,
-                                                           kind=kind,
-                                                           ios_app_id=ios_app_id)
+                                                           defaults=dict(
+                                                               kind=kind,
+                                                               ios_app_id=ios_app_id))
     if not created:
         token.last_updated = now()
         token.save(update_fields=['last_updated'])