Make hiera::eyaml defaults come from base class

The hiera::eyaml defaults were coming from hiera::params, but so were
the defaults for the eponymous class. This requires passing the same
parameters to both classes.

This change lets the eyaml class pull the defaults from the eponymous
class and therefore not need duplicate values passed.
Merge pull request #40 from hunner/eyaml_defaults

Make hiera::eyaml defaults come from base class