(MODULES-1383) Add restart parameter

This commit adds a restart parameter to both postgresql::server and postgresql::server::config_entry.

When set to true, a restart of the postgresql service will be preferred when changing config settings, rather than a reload. The parameter in server::config_entry takes the value set in postgresql::server by default, but can be set independently.

I'm open to suggestions in making the code less kludgy.
Should more rspec tests be added?