(GEP-172) Support resource body with arbitrary rvals in title

Puppet versions >= 4.0 will allow using arbitrary rvalue expressions
as the title in resource bodies. This commit ensures that Geppetto
doesn't complain about such expressions unless the target platfrom
is < 4.0.
I don't get this test. It is called ValidateExpressionTitlesNotOk, shy does it then use a * => $h construct? What is being tested here?