Due to Python's GIL [1], we can't use multiple threads for running
OpenStack services without a performance penalty, since the execution
ends up serialized, which defeats the purpose.
Instead, we should use several processes, since this approach doesn't
have this limitation.
[1] https://wiki.python.org/moin/GlobalInterpreterLock
Change-Id: I3aa3757a991d4437d0921cb55c1d08b5c9179de1