engine: TimeoutBase - Improving memory footprint - continue

After changes inside TimeoutBase, I found out that the cache is used only as place holder,
so instead of putting TimeouBase object to cache I decided to put String, also possible to put
some king const Object but, I think it is not make any difference
Benefit - String should take less memory than TimeoutBase will all loaded objects from DB

Change-Id: I795019a35a57fef688296d9f1083bc77c9272bc7
Signed-off-by: Michael Kublin <mkublin@redhat.com>