Updated default.rb to assume ENV['PATH'] is sufficient to specify cpan a...

Removed '/usr/bin' portions of commands and sets because different systems may have these binaries in different places of PATH. Relying on ENV['PATH'].

Also added a confine since the osfamily supported set is restricted to Debian and RedHat types. The original module isn't making use of :osfamily which a pending pull request will change the case statement to use this fact in init.pp.