Expose systemd service properties via .info

[alexpop]

Systemd has lots of properties that this PR is exposing now. Usage example:

describe service('sshd').info[:properties]['Restart'] do
  it { should cmp 'on-failure'  }
end

[chris-rock]

This looks good @alexpop
Be aware, that the test, may crash if service('sshd').info[:properties]['Restart'] is not available. Therefore info is nil

[alexpop]

For systemd, the service resource will still be instantiated, even for missing services:

inspec> service('BOGUSSSSSSSSS').info[:properties]['Restart']
=> "no"
inspec> service('BOGUSSSSSSSSS').info
=> {:name=>"BOGUSSSSSSSSS.service",
 :description=>"BOGUSSSSSSSSS.service",
 :installed=>false,
 :running=>false,
 :enabled=>false,
 :type=>"systemd",
 :properties=>
  {"Type"=>"",
   "Restart"=>"no",
   "PIDFile"=>"",
   "NotifyAccess"=>"none",

[arlimus]

@alexpop To Chris' point, if these were to run on e.g. an old Debian system, where we are not based on Systemd, or if any of the calls don't get through, we will have info == nil.

[alexpop]

Correct, but we only generate tests like that from SCAP systemdunitproperty_test resources.