Fix deprecation warnings in Config spec

RSpec 2.99.1 was complaining about our use of `be_false`/`be_true`. Make
it happy.

Change-Id: Ia505faa79dfb65a3b5fe4385aacca53800bc4844
Reviewed-on: http://gerrit.causes.com/39136
Tested-by: jenkins <jenkins@causes.com>
Reviewed-by: Shane da Silva <shane.dasilva@brigade.com>