Test coverage improvement for LBaaS screens

This patch set adds tests for 'delete' actions and
removes some unused methods from @test.create_stubs.

Closes-Bug: #1268926

Change-Id: I83724ea3a6d424e01ab10061e5db5c8350ab2174
Fixes create flavor extras success_url

Change success_url "http://${ip}/admin/flavors/1/extras/" to
"http://${ip}/${LOGIN_REDIRECT_URL}/admin/flavors/1/extras/"

Closes-Bug:#1268860

Change-Id: I874d0e3a4c065097cfb4ed7572ac5df335b1ed96
Merge "Test coverage improvement for LBaaS screens"
Merge "Fixes create flavor extras success_url"