Fix fake_update in test_update_missing_server

In test_update_missing_server, fake_update should be used as update()
method but it is used as create() instead. In addition, the test comment
also is wrong.
This patch fixes them.

Change-Id: Ia4704413dd7355010546dba7096ed34225bb4b0f
Merge "Fix fake_update in test_update_missing_server"