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>