(#13009) Compare scheduled task commands using backslashes

Previously, if the command for a scheduled task was specified using
forward slashes, puppet would always think the resource was out-of-sync.
This issue is that Windows does not preserve forward slashes, so the
*current* value always contains backslashes.

This commit munges forward slashes in the command to backslashes. It also
uses File.expand_path, because otherwise commands like the following in
the puppet language would be considered different:

command => 'c:\\windows\\system32\\cmd.exe'
command => 'c:\windows\system32\cmd.exe'