Correct return values of mocked methods in LBaaS API test

Mocked methods of neutronclient should return data structure
which neutronclient returns, but Horizon internal API object
(which inherits APIDictWrapper) is returned so far.

Change-Id: Ifbaeea3234bc232c8bbd2bb6ed2dd8f236358d1b
Closes-Bug: #1360279
Merge "Correct return values of mocked methods in LBaaS API test"