Moving params.pp parameters as class parameters.

This doesn't change the behavior of parameters inheritance.

Meanwhile it allows hierarchical lookups which are now available by
default from Puppet Version 3.x.
So for instance /var/lib/hiera/defaults.yaml could contain:
quickstack::params::admin_password: CHANGEME
quickstack::params::verbose: true
Merge pull request #301 from gildub/parameters+inheritance

Moving params.pp parameters as class parameters.