There is an issue with classloaders while running the test module from
java.
It works when run directly by golo.

Here I switch the current thread classloader. Works fine, but there
should be a better approach (thread local singleton for
`Runtime.classLoader()`.

Define a thread local variable to hold the current thread classloader.

When running from golo, the current thread classloader will be a
GoloClassLoader instance, so it is used as is.
The issue is that when running from Java, the current classloader is not
a golo one, so it was wrapped by `Runtime.classLoader()`. We
therefore got a different one for each call.
Keeping it in a thread local singleton resolve this issue.