Add db.conn.log option to suppress sql logs by default

The Store logging is quite verbose with a flurry of
init and destroy messages with each session. Setting
db.conn.log to False (default) will suppress these. If one
needs to do connection tracing it can be enabled.

Signed-off-by: Rob Crittenden <rcritten@redhat.com>
Reviewed-by: Simo Sorce <simo@redhat.com>