dsc_lite : Puppet runs fail on a host with 1.10 agent packages (Puppet 4) and WMF < 5

Due to changes that were made in Puppet 5, code intended to generate warnings for an outdated PowerShell version will cause runs to completely fail.

The dsc_lite feature calls the Puppet.warn_once method to only display the inadequate WMF5 version once. In Puppet 5, that method takes 6 parameters. In Puppet 4, the method only took 5 parameters.

See the change that landed in:
https://github.com/puppetlabs/puppet/commit/3d823370884f032368d118e045af86bf54386a63

2 options were vetted for addressing this problem:

• Call Puppet.err instead of Puppet.warn_once. This was tested and produced error messages for every single dsc_lite resource, which is undesirable.
• Vary the call to warn_once based on the method arity. This results in warning messages on Puppet 4 and error messages on Puppet 5, but at least limits their count to a single message.

We opted for the latter as it's less intrusive.