Tune default parameters for pid_file, daemon user/group, include_dir on Gentoo system

Default arguments handled according to http://docs.puppetlabs.com/guides/style_guide.html#class-parameter-defaults
Handle 'amd64' architecture

According to http://docs.puppetlabs.com/facter/1.6/core_facts.html#architecture
Merge pull request #11 from vrutsky/gentoo_support

Tune default parameters for Gentoo