disable mroonga temporarily: see MDEV-7246

debian/dist/Debian/mariadb-server-10.1.files.in

 usr/lib/mysql/plugin/auth_pam.so
 usr/lib/mysql/plugin/auth_socket.so
-usr/lib/mysql/plugin/ha_mroonga.so
 usr/lib/mysql/plugin/ha_sequence.so
 usr/lib/mysql/plugin/ha_sphinx.so
 usr/lib/mysql/plugin/ha_innodb.so

debian/dist/Ubuntu/mariadb-server-10.1.files.in

 usr/lib/mysql/plugin/auth_pam.so
 usr/lib/mysql/plugin/auth_socket.so
-usr/lib/mysql/plugin/ha_mroonga.so
 usr/lib/mysql/plugin/ha_sequence.so
 usr/lib/mysql/plugin/ha_sphinx.so
 usr/lib/mysql/plugin/ha_innodb.so

storage/mroonga/CMakeLists.txt

@@ -240,16 +240,12 @@ link_directories(
 
 if(MRN_BUNDLED)
   if(GROONGA_NORMALIZER_MYSQL_FOUND AND MRN_GROONGA_BUNDLED)
-    mysql_add_plugin(mroonga
-      "${MROONGA_SOURCES};${MRN_UDF_SOURCES};${MRN_GRN_NORMALIZER_MYSQL_SOURCES};${LIBMRN_NEED_MYSQL_SOURCES};${LIBMRN_NO_MYSQL_SOURCES}"
-      STORAGE_ENGINE MODULE_ONLY
-      LINK_LIBRARIES ${GROONGA_LIBRARIES})
+    set(sources "${MROONGA_SOURCES};${MRN_UDF_SOURCES};${MRN_GRN_NORMALIZER_MYSQL_SOURCES};${LIBMRN_NEED_MYSQL_SOURCES};${LIBMRN_NO_MYSQL_SOURCES}")
   else()
-    mysql_add_plugin(mroonga
-      "${MROONGA_SOURCES};${MRN_UDF_SOURCES};${LIBMRN_NEED_MYSQL_SOURCES};${LIBMRN_NO_MYSQL_SOURCES}"
-      STORAGE_ENGINE MODULE_ONLY
-      LINK_LIBRARIES ${GROONGA_LIBRARIES})
+    set(sources "${MROONGA_SOURCES};${MRN_UDF_SOURCES};${LIBMRN_NEED_MYSQL_SOURCES};${LIBMRN_NO_MYSQL_SOURCES}")
   endif()
+  mysql_add_plugin(mroonga ${sources} STORAGE_ENGINE MODULE_ONLY LINK_LIBRARIES ${GROONGA_LIBRARIES}
+    DISABLED)
  else()
 else()
   add_library(mroonga MODULE