Regression : ensure threads names are not modified (eg. by Jython)

Regression from d564f0aa49624a2e7af5ab399b4a0e66d5979160

Making some "Not a worker thread" exceptions because Jython does rename vert.x-worker-thread-x to MainThread.

Signed-off-by: Julien <jlehuraux@chyro.fr>