During working with python3-first goals, I have notticed the
log_generator and log_save methods was non compliance with python3.
This is what doesn't appears in integration tests because we execute
only trove-functional-mysql job which doesn't covers guest-log tests.
In separate change I will extend zull definition by scenario tests to
avoid similar issues in future.
Change-Id: If85dff57afe110991553d510c6af4468a6781f64
Signed-off-by: Marcin Piwowarczyk <m.piwowarczy@samsung.com>