Fix py26 timeouts

tests.benchmark.test_runner.test_run_scenario_exception_inside_test
sometimes produce gate timeouts (worked more then 60 minutes)

Seems like the issues was related to the way we use mock.

Change-Id: I96c79b4d6d321931015413e7a308ddd3d1d83f20
Closes-Bug: #1271831
Merge "Fix py26 timeouts"