Bug 17913: Adjust merge test for AuthorityMergeMode

Bug 17913: Adjust merge test for AuthorityMergeMode

Original fix from a patch on bug 11315.
Amended by Marcel de Rooy January 2017.

Test plan:
Run t/db_dependent/Authorities/Merge.t in both loose and strict mode.
Should no longer make a difference.

Signed-off-by: Marcel de Rooy <m.de.rooy@rijksmuseum.nl>
Signed-off-by: Josef Moravec <josef.moravec@gmail.com>
Signed-off-by: Julian Maurice <julian.maurice@biblibre.com>
Signed-off-by: Kyle M Hall <kyle@bywatersolutions.com>