Fix test regression introduced by 976ba90
Add support for parameter overrides

 * Add hiera support to varnish::install
 * Add hiera support to varnish::repo
 * Fix varnish::params::packages to install varnish and libvarnishapi1
 * Update README/tests
Update class parameters, confine to init class

 * Centralize the parameters in the init class instead of scattered
   throughout classes it invokes.
 * Add puppetdoc parameter info.
 * Update README, resource collectors can still be used but are
   generally not advised.