Fix printing of empty tables
Fix printing of empty tables

When trying to print an empty DB table, the
exception is thrown even that the table exists
its just empty.
This patch change this to print empty list
instead

Change-Id: I8bb73fbe943b027fb8d907f317da4a5aefcad477

FrankDuan/df_code,FrankDuan/df_code,openstack/dragonflow,openstack/dragonflow,FrankDuan/df_code,openstack/dragonflow