agent.pp and server.pp inherit puppet::params
Improve the package installation

Move all package installation related operations to package.pp
Improve the condition on where to install the puppet package on master
It is based if the puppet package name is different in agent and master,
and if the specific node is a master ($puppet::server::master = true variable)
Add full Gentoo support

Supports usage of USE flags, KEYWORDS and package installation
Introduces dependency to adrienthebo/portage module
Remove line that seems invalid