Fix pep8
Fix pep8

Fix pep 8 in test_mixin file
Change-Id: I5afb2fd9fd722b4cef6d1d099574f13c63215252

mcloudv/fuel-ostf,mcloudv/fuel-ostf,eayunstack/fuel-ostf,stackforge/fuel-ostf,eayunstack/fuel-ostf,stackforge/fuel-ostf