[CdiControl] cdictrl-owb should only use the Session mocks if the servlet-api is available

currently cdictrl-owb mandatorily needs the servlet-api on the classpath. But this is in fact only needed if the openwebbeans-web plugin is being used which automatically brings a servlet based cdi lifecycle plugin with it.

So if we don't have the servlet-api on the ClassPath, we don't need to create any Session and ServletContext mocks at all.