Fix cells instance_create extra kwarg

When the API cell receives a message to update an instance, it'll try to
create it if it doesn't already exist in order to sync up.  However,
it's calling db.instance_create with an extra kwarg that doesn't exist
and failing.  This patch removes the extra kwarg.

The bug was introduced in this change id:

Ife5be9922db0742c8ee4f970517396be86597cce

Change-Id: I69bcb3dda2cbb566b0d69c5eac005703654ea811
Closes-bug: 1247919
Merge "Fix cells instance_create extra kwarg"