etl: fixed issue with user_logged_in_to_guest column null handling

etl did not handle null values well, this is now fixed.

Change-Id: Ib70d02aaf4d8de4f6f6af6d3ce1b5f511e64c3a8
Bug-Url: https://bugzilla.redhat.com/1057412
Signed-off-by: Yaniv Dary <ydary@redhat.com>