put ha_xtradb.so in deb packages

debian/dist/Debian/mariadb-server-10.0.files.in

@@ -2,6 +2,7 @@ usr/lib/mysql/plugin/auth_pam.so
 usr/lib/mysql/plugin/auth_socket.so
 usr/lib/mysql/plugin/ha_sequence.so
 usr/lib/mysql/plugin/ha_sphinx.so
+usr/lib/mysql/plugin/ha_xtradb.so
 usr/lib/mysql/plugin/handlersocket.so
 usr/lib/mysql/plugin/locales.so
 usr/lib/mysql/plugin/metadata_lock_info.so

debian/dist/Ubuntu/mariadb-server-10.0.files.in

 usr/lib/mysql/plugin/auth_pam.so
 usr/lib/mysql/plugin/auth_socket.so
 usr/lib/mysql/plugin/ha_sequence.so
-usr/lib/mysql/plugin/ha_sphinx.so
+usr/lib/mysql/plugin/ha_xtradb.so
 usr/lib/mysql/plugin/handlersocket.so
 usr/lib/mysql/plugin/locales.so
 usr/lib/mysql/plugin/metadata_lock_info.so