Fix crontab that use month of year and day of month

This patch fix the use of periodic tasks with
both month_of_year and day_of_month.

Before this patch, in July for a tasks that should
run in February, the periodic task run again and
again. Celery believes it is 5 months late when
it is 7 month in advance.
Removes error at end of test run from kombu memory backend QoS sanity assertions