(#56) notify service to restart on plugin install

See if we're managing a server, and if so set notifications from the package
resource or File[$mcollective::site_libdir].

This isn't excercised by the rspec-puppet tests, as there's no way
to test for resource relationships currently with rspec-puppet.
Maybe if rodjek/rspec-puppet#106 were merged.
Merge pull request #61 from richardc/bug/master/56

(#56) notify service to restart on plugin install