HPCC-12761 Fix memcachedtest xml key

Signed-off-by: James Noss <james.noss@lexisnexis.com>
Merge pull request #6774 from jamienoss/issue12761-fix-memcachedtest.xml

HPCC-12761 Fix memcachedtest xml key

Reviewed-by: Gavin Halliday <ghalliday@hpccsystems.com>