[AIRFLOW-7001] Time zone removed from MySQL TIMSTAMP field inserts
[AIRFLOW-7001] Time zone removed from MySQL TIMSTAMP field inserts

For mysql we should store timestamps as naive values.

Timestamp in MYSQL is not timezone aware. In MySQL 5.6
timezone added at the end is ignored but in MySQL 5.7
inserting timezone value fails with 'invalid-date'

(cherry picked from commit e7d65661ba569b148cd3d560a00883392935b01d)

owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow,owlabs/incubator-airflow