all member of random module are available (because in ZopeGuards, there's a
random.__allow_access_to_unprotected_subobjects__ = 1), SystemRandom class
also is, but Random class was not, even though there should be nothing unsafe
in this.

This is needed if we want to use a random number generator with a fixed seed
to get reproductible results. We could use random.seed module level function
but since this is also used by several things in ERP5 this does not produce
reproductible sequences.