Add new type service_config

Solaris 11 has migrated a log of configuration parameters from
configuration files into smf manifests. So instead of manipulating the file
`/etc/resolv.conf` to define your nameservers you manipulate properties with the svccfg utility.

The new type `service_config` can now be used to set such properties,
e.g.:

    service_config { 'config/nameserver':
      ensure => [ '10.0.0.2', '10.0.0.3' ],
      fmri   => 'svc:/network/dns/client',
      type   => net_address,
    }

Because I was not able to test the puppet type and provider with the current spec helper, I followed the instructions on https://github.com/puppetlabs/puppetlabs_spec_helper to include the puppet spec helper.