Revert: Change of type from void* to CookieIface* for engine_data

Revert an incorrect change from void* to CookieIface* for the
engine_data arg of store_engine_specific().

Change-Id: I8dfb5c45ab18bb7b9c826e4e064779e3df3b400b
Reviewed-on: http://review.couchbase.org/c/kv_engine/+/155820
Tested-by: Build Bot <[email protected]>
Reviewed-by: Dave Rigby <[email protected]>

Author: rdemellow

include/memcached/engine_testapp.h

@@ -119,7 +119,7 @@ struct test_harness {
      * Store the specified pointer in the specified cookie
      */
     virtual void store_engine_specific(const CookieIface* cookie,
-                                       CookieIface* engine_data) = 0;
+                                       void* engine_data) = 0;
 
     /**
      * Get the number of references for the specified cookie

programs/engine_testapp/engine_testapp.cc

@@ -193,7 +193,7 @@ class MockTestHarness : public test_harness {
     }
 
     void store_engine_specific(const CookieIface* cookie,
-                               CookieIface* engine_data) override {
+                               void* engine_data) override {
         get_mock_server_api()->cookie->store_engine_specific(cookie,
                                                              engine_data);
     }