Update scheduled tasks if definition changed

With this patch, when we update the command or the user, and if we set
"force" to true, then the scheduled task is updated.

BTW, I see in https://github.com/opscode-cookbooks/windows/blob/master/CONTRIBUTING that I should open a Jira task to contribute. However, according to http://www.getchef.com/blog/2014/06/16/chef-issue-tracking-and-contribution-workflow-updates/ I believe that this file is outdated. Please feel free to tell me If I'm wrong.
Here are why I don't want to use cleanpath:
* The `cleanpath` method is only available on chef version >=12
* It does not handle double quotes
* It'll replace all forwardslashes into backslashes (we do not want to modify the command here)