[AIRFLOW-27] Fixed MsSql autocommit bug

[biellls]

Dear Airflow Maintainers,

Please accept this PR that addresses the following issues:

• https://issues.apache.org/jira/browse/AIRFLOW-27

Reminders for contributors:

• Your PR's title must reference an issue on Airflow's JIRA. For example, a PR called "[AIRFLOW-1] My Amazing PR" would close JIRA issue Improving the search functionality in the graph view #1. Please open a new issue if required!
• You must add an Apache License header to all new files.
• Please squash your commits when possible and follow the 7 rules of good Git commits.

[landscape-bot]

Repository health increased by 0.01% when pulling e7e655f on biellls:master into 03aa500 on airbnb:master.

• No new problems were introduced.
• 1 problem was fixed (including 0 errors and 0 code smells).

[coveralls]

Coverage decreased (-0.02%) to 67.136% when pulling e7e655f on biellls:master into 03aa500 on airbnb:master.