[Ruby] Share and manage one singleton scripting container.

As this is a very heavy weight component, but the
gateway itself is not thread safe (according to Kristian)

CI
http://bamboo.s/browse/NX-OSSF317
there is no need for the OSGiScriptingContainer since the regular ScriptingContainer will do the job and with newer jruby versions the regular ScriptingContainer is already the better choice for OSGi environments.