Fix puppet-neutron rspec test for RSpec >= 3.0.0

Since rspec 3.0.0.beta1 (2013-11-07) be_true and be_false
are now renamed to be_truthy and be_falsey.

Closes-bug #1326034
Change-Id: I6ca0d3f7529c6d4596ab10dd9e55157bad9ace86