install client plugins into their old location

cmake/mariadb_connector_c.cmake

@@ -47,5 +47,7 @@ ELSE()
   SET(CONC_INSTALL_LAYOUT "DEFAULT")
 ENDIF()
 
+SET(PLUGIN_INSTALL_DIR ${INSTALL_PLUGINDIR})
+
 MESSAGE("== Configuring MariaDB Connector/C")
 ADD_SUBDIRECTORY(libmariadb)

debian/libmariadbclient18.files

 usr/lib/mariadb/libmariadb.so.*
-usr/lib/mariadb/plugin/mysql_clear_password.so
-usr/lib/mariadb/plugin/dialog.so
+usr/lib/mysql/plugin/mysql_clear_password.so
+usr/lib/mysql/plugin/dialog.so

debian/mariadb-gssapi-client-10.2.files

-usr/lib/mariadb/plugin/auth_gssapi_client.so
+usr/lib/mysql/plugin/auth_gssapi_client.so