Some minor fixes for the Paludis package provider

- only search for non-masked packages
- increased the command timeout for the installation process to a reasonable large number
This is a pretty large timeout value compared to some of the other package providers such as apt, which defaults to 15 min. Package resource now has a timeout attribute -- can you use that here? If the default needs to be higher for Paludis, you could create a paludis_package similar to apt_package to encourage that policy.