[AIRFLOW-1613] Make MySqlToGoogleCloudStorageOperator compaitible with python3
[AIRFLOW-1613] Make MySqlToGoogleCloudStorageOperator compaitible with python3

Closes #2609 from jgao54/make-MySqlToGoogleCloudStorageOperator-python3-compaitible

Twistbioscience/incubator-airflow,Twistbioscience/incubator-airflow,Twistbioscience/incubator-airflow,Twistbioscience/incubator-airflow