Avoid building not needed engine.

oqgraph will be automatically built when libboost is available. In order to
follow separation from operating system avoid to building this not needed engine
and thus do not depend on operating system's library.

component/mariadb/buildout.cfg

@@ -46,6 +46,7 @@ configure-options =
   --with-plugins=max-no-ndb
   --with-aria-tmp-tables
   --without-plugin-innodb_plugin
+  --without-plugin-oqgraph
   --without-readline
   --with-ssl
   --with-libevent=${libevent:location}