Fix for #2267

During UVE sync, the UVE object is initialized with the sandesh_global instance during creation.
If the sandesh client doesn't call init_generator() on the sandesh_global instance, then the sandesh_global
instance will have empty source, node_type, module and instance_id. Therefore, UVE object initialized with
the sandesh_global instance will be sent with empty source, node_type, module and instance_id in the sandesh header. This results in improper addition/updation/deletion of UVEs in redis.
In sync_uve(), pass sandesh_instance while creating UVE object.