splunk running as non-root user

new splunk installations can run as a non-root user if desired (this cookbook does not support switching between root and non-root, should it?)

There is a really ugly ruby_block which I tried pushing to a definition, spent 2+ days trying to get it to work, and then giving up.  We may even be able to skip this recursive chown if we can determine which of the Execute resources is spraying root owned files into $SPLUNK_HOME.

There are no tests for this change.  Should there be?
So I think we can consolidate this with by modifying the execute above.

```ruby
execute "#{splunk_cmd} enable boot-start --accept-license --answer-yes" do
  unless node['splunk']['server']['runasroot']
    command "#{splunk_cmd} enable boot-start --accept-license --answer-yes -user #{node['splunk']['user']['username']}"
    not_if 'grep -q /bin/su /etc/init.d/splunk'
    only_if node['splunk']['is_server']
  end
  not_if { ::File.exist?('/etc/init.d/splunk') }
end
```

This has two benefits:

1. We have a single resource for managing a single thing (the init script creation).
2. We stay within the accept license attribute guard.

I think the comment should be moved to the README as a description of what the attribute does (bonus: we get documentation).