test/test_cors.cc: initialize key_type in constructor

CID 1019635 (#1 of 1): Uninitialized pointer field (UNINIT_CTOR)
  uninit_member: Non-static class member "kt" is not initialized in
  this constructor nor in any functions that it calls.

Signed-off-by: Danny Al-Gaaf <danny.al-gaaf@bisect.de>