This allows to setup an almost fully functional cluster without additional
processes. Threads are scheduled so that they never run simultaneously,
eliminating most random.
There's still much improvement possible like controlled randomization,
or easier debugging when switching from one thread to another.

As mock objects are not usable in such tests, an API should be implemented to
trace/count any method call we'd like to check.

This fixes test_notifyNodeInformation_checkUnregisterStorage

git-svn-id: https://svn.erp5.org/repos/neo/trunk@2775 71dcc9de-d417-0410-9af5-da40c76e7ee4