Cells: Send instance object for instance_delete_everywhere

The delete method in the compute api expects an instance object to be
passed in. So the instance object needs to not be to_primitived in the
instance_delete_everywhere rpc method.

Change-Id: I620ec57bc28ba11335758455c7cac0bfa63f5b37
Closes-bug: #1293750
Merge "Cells: Send instance object for instance_delete_everywhere"