Fix systemd support and service subclass ordering

[treydock]

Pull Request (PR) description

Fix execution of splunk enable boot-start to actually work with systemd systems and also to not specify -user when root is the user and also supporting systemd to avoid unnecessary chown lines in unit file per 7.3.2 docs.

Also fix order of service subclasses so they are applied after packages and configs.

This Pull Request (PR) fixes the following issues

Fixes #262
Fixes #263

[treydock]

For #263, with this PR the behavior is correct, the package upgrade took place before executing splunk commands.

Notice: /Stage[main]/Splunk::Forwarder::Install/Package[splunkforwarder]/ensure: ensure changed '7.1.1-8f0ead9ec3db' to '0:7.3.2-c60db69f8e32'
Info: Computing checksum on file /etc/init.d/splunk
Info: /Stage[main]/Splunk::Forwarder::Config/File[/etc/init.d/splunk]: Filebucketed /etc/init.d/splunk to puppet with sum b5f8f145d4dd1ce725dc3dcdcab05980
Notice: /Stage[main]/Splunk::Forwarder::Config/File[/etc/init.d/splunk]/ensure: removed
Info: Class[Splunk::Forwarder::Config]: Scheduling refresh of Class[Splunk::Forwarder::Service]
Info: Class[Splunk::Forwarder::Service]: Scheduling refresh of Class[Splunk::Forwarder::Service::Nix]
Info: Class[Splunk::Forwarder::Service]: Scheduling refresh of Service[SplunkForwarder]
Info: Class[Splunk::Forwarder::Service::Nix]: Scheduling refresh of Exec[stop_splunkforwarder]
Info: Class[Splunk::Forwarder::Service::Nix]: Scheduling refresh of Exec[enable_splunkforwarder]
Notice: /Stage[main]/Splunk::Forwarder::Service::Nix/Exec[stop_splunkforwarder]/returns: executed successfully (corrective)
Info: /Stage[main]/Splunk::Forwarder::Service::Nix/Exec[stop_splunkforwarder]: Scheduling refresh of Exec[enable_splunkforwarder]
Notice: /Stage[main]/Splunk::Forwarder::Service::Nix/Exec[stop_splunkforwarder]: Triggered 'refresh' from 1 event
Info: /Stage[main]/Splunk::Forwarder::Service::Nix/Exec[stop_splunkforwarder]: Scheduling refresh of Exec[enable_splunkforwarder]
Notice: /Stage[main]/Splunk::Forwarder::Service::Nix/Exec[enable_splunkforwarder]: Triggered 'refresh' from 3 events
Notice: /Stage[main]/Splunk::Forwarder::Service/Service[SplunkForwarder]/ensure: ensure changed 'stopped' to 'running'
Info: /Stage[main]/Splunk::Forwarder::Service/Service[SplunkForwarder]: Unscheduling refresh on Service[SplunkForwarder]