Fix systemd service enabled check

[jmccann]

I believe the wrong param from systemctl show is being checked to determine if a service is enabled/disabled in systemd.

Currently I have tests passing as enabled when I have a service disabled in systemd:

describe service('corosync') do
  it { should be_running }
  it { should be_enabled }
end

Is passing when I see the following from systemd:

[root@default-centos-71 ~]# systemctl status corosync
corosync.service - Corosync Cluster Engine
   Loaded: loaded (/usr/lib/systemd/system/corosync.service; disabled)
   Active: active (running) since Mon 2016-01-11 21:02:11 UTC; 32min ago
 Main PID: 13283 (corosync)
   CGroup: /system.slice/corosync.service
           └─13283 corosync

Notice how in Loaded at the end it shows 'disabled'.

Also, please see the ActiveState vs UnitFileState when enabling and disabling the service with systemd:

[root@default-centos-71 ~]# systemctl show --all corosync | grep -e UnitFileState -e ActiveState
ActiveState=active
UnitFileState=disabled
[root@default-centos-71 ~]# systemctl enable corosync
ln -s '/usr/lib/systemd/system/corosync.service' '/etc/systemd/system/multi-user.target.wants/corosync.service'
[root@default-centos-71 ~]# systemctl show --all corosync | grep -e UnitFileState -e ActiveState
ActiveState=active
UnitFileState=enabled
[root@default-centos-71 ~]# systemctl disable corosync
rm '/etc/systemd/system/multi-user.target.wants/corosync.service'
[root@default-centos-71 ~]# systemctl show --all corosync | grep -e UnitFileState -e ActiveState
ActiveState=active
UnitFileState=disabled

This PR addresses the issue by updating the check to use param UnitFileState to check if the service is enabled or disabled instead of ActiveState.

[chris-rock]

Thanks for fixing this @jmccann