Fix a copy/pasted test mistake

Fix a minor test mistake that was copied around a few times.  In mock
setup, the intention was to only return a value of the rpc method used
was a 'call', not 'cast'.  Unfortunately, the variable checked was
method instead of rpc_method, so this expected return was always set
to None.

This also points out that what's being tested here isn't what *really*
was intended.  It ends up testing that the code returns what we mocked
it to return, which isn't all that useful.  However, at least with
this fix it's a bit more clear what it's trying to do.

Change-Id: I18e85aa66f83331318177d70cbae2468ff8bb57d

neutron/tests/unit/hyperv/test_hyperv_rpcapi.py

@@ -34,7 +34,7 @@ class rpcHyperVApiTestCase(base.BaseTestCase):
     def _test_hyperv_neutron_api(
             self, rpcapi, topic, method, rpc_method, **kwargs):
         ctxt = context.RequestContext('fake_user', 'fake_project')
-        expected_retval = 'foo' if method == 'call' else None
+        expected_retval = 'foo' if rpc_method == 'call' else None
         expected_version = kwargs.pop('version', None)
         expected_msg = rpcapi.make_msg(method, **kwargs)
 

neutron/tests/unit/ml2/test_rpcapi.py

@@ -167,7 +167,7 @@ class RpcApiTestCase(base.BaseTestCase):
 
     def _test_rpc_api(self, rpcapi, topic, method, rpc_method, **kwargs):
         ctxt = context.RequestContext('fake_user', 'fake_project')
-        expected_retval = 'foo' if method == 'call' else None
+        expected_retval = 'foo' if rpc_method == 'call' else None
         expected_version = kwargs.pop('version', None)
         expected_msg = rpcapi.make_msg(method, **kwargs)
 

neutron/tests/unit/mlnx/test_rpcapi.py

@@ -32,7 +32,7 @@ class rpcApiTestCase(base.BaseTestCase):
     def _test_mlnx_api(self, rpcapi, topic, method, rpc_method,
                        expected_msg=None, **kwargs):
         ctxt = context.RequestContext('fake_user', 'fake_project')
-        expected_retval = 'foo' if method == 'call' else None
+        expected_retval = 'foo' if rpc_method == 'call' else None
         expected_kwargs = {}
         if topic:
             expected_kwargs['topic'] = topic