Fix usage of rest_client expected_success() in tests

rest_client expected_success() method expect read_code
must be int and states the same in doc string .

Tempest is converting that to error instead of false pass.
Details: I3f4c58bdbb172805514831103927d3464d65d7f3

Change-Id: Ic4b0af5701df99621e3abb693644c4824c92dc4c
1 file changed