core: Adding unit test for DnsLocator

The purpose of the second test is to cause contract
breakage of compareTo, based on data attached to the bug
Bug-Url: https://bugzilla.redhat.com/985623

Change-Id: Ied8ca585b38d624c04b3f232833e1b34ad5dfab5
Signed-off-by: Yair Zaslavsky <yzaslavs@redhat.com>