Fix db reconnect issue under django 1.6+

Django's orm layer will not auto-reconnect after it looses
the connection to the mysql server, until you manually close the
database connection in django 1.6 and above.

(see: https://code.djangoproject.com/ticket/21597)

This is an issue for persistant connections, as MySQL will timeout
inactive connections, and any loss of the db connection will cause
the stacktach worker to simply repeat the error
"MySQL server has gone away" until restarted.

This fix will allow the stacktach worker to properly reconnect.

Change-Id: I0b0bc75b7e21fd183f3b0e7a55d727ff98d6f02b