remove extra whitespaces
clean up classloader type hierachy

* only the classloader runtime.getJRubyClassLoader needs to have
  all the extra features. all other classloaders just needs to
  be able to define classes and do not need the extra overhead of
  loading and finding resources and adding jar files during runtime.
* the OneShotClassloader is only used with runtime.getJRubyClassLoader
  so ensure this relation via types
* the JRubyClassLoader is used at various places also as "flag via instanceof".
  keep this and all other uses of JRubyClassLoader as it was before
* replace on use of OneShotClassloader with JRubyClassLoader to check if it possible
  to load byte code at runtime
fix -Pjruby_complete_jar_extended
Revert "[build] check_versions.sh does not need to -Pboostrap - save some CPU cycles"

This reverts commit 48a12f53f55418d7aa26dc0b7cf1ee070712a217.