Simplify a YAML report test to work with Ruby 1.9

The order of invocation of local method definition and the parent inherited
hook changed between 1.8 and 1.9, resulting in the hack that works around a
development check in this test stopping working.

None of that ceremony is actually needed, though, since we can totally just
use an instance of the actual class we are testing.

Signed-off-by: Daniel Pittman <daniel@puppetlabs.com>