(MODULES-6860) Add dsc_lite feature for confines

 - Previously when a version of PowerShell older than 5.0.10586.117
   was installed, Puppet would return an error message like:

   Error: Could not find a suitable provider for dsc

   Unfortunately this message did not yield any useful information,
   even with --debug and --verbose turned on, because of the way the
   existing confine check was performed with a confine :true

   To produce a more useful message that is meaningful to users,
   introduce a new feature that performs the same check as the
   confine, but that also will issue an error message (only once)
   that indicates the installed version / required version constraints
   for the module, changing the output to:.

   Error: The dsc_lite module requires PowerShell version 5.0.10586.117 - current version 5.0.10514.6\n   (file & line not available)
   Error: Could not find a suitable provider for dsc

 - Note that DSC_LITE_MODULE_POWERSHELL_UPGRADE_MSG is never actually
   shown when the PowerShell version is < 5.0.10586.117 because the
   check occurs too late in the lifecycle of loading providers. The
   confine code has already evaluated, preventing the other messsages
   from being shown.

lib/puppet/feature/dsc_lite.rb

@@ -0,0 +1,20 @@
+require 'puppet/util/feature'
+
+if Puppet.features.microsoft_windows?
+  required_version = Gem::Version.new('5.0.10586.117')
+  installed_version = Gem::Version.new(Facter.value(:powershell_version))
+
+  if (installed_version >= required_version)
+    Puppet.features.add(:dsc_lite)
+  else
+    Puppet.warn_once(
+      'dsc_lite_unavailable',
+      :dsc_lite_unavailable,
+      _("The dsc_lite module requires PowerShell version %{required} - current version %{current}") %
+        { :required => required_version, :current => installed_version},
+      nil,
+      nil,
+      :err
+    )
+  end
+end

lib/puppet/type/dsc.rb

@@ -20,7 +20,7 @@
       fail("#{value} is not a valid #{self.name.to_s}") unless value =~ /^[a-zA-Z0-9\.\-\_\'\s]+$/
     end
   end
-  
+
   newparam(:dsc_resource_name) do
     desc "DSC Resource Name"
     isrequired
@@ -66,7 +66,7 @@
 end
 
 Puppet::Type.type(:dsc).provide :powershell, :parent => Puppet::Type.type(:base_dsc_lite).provider(:powershell) do
-  confine :true => (Gem::Version.new(Facter.value(:powershell_version)) >= Gem::Version.new('5.0.10586.117'))
+  confine :feature => :dsc_lite
   defaultfor :operatingsystem => :windows
 
   mk_resource_methods

tests/files/dsc_puppetfakeresource/dsc_puppetfakeresource.rb

@@ -126,7 +126,7 @@ def builddepends
 end
 
 Puppet::Type.type(:dsc_puppetfakeresource).provide :powershell, :parent => Puppet::Type.type(:base_dsc_lite).provider(:powershell) do
-  confine :true => (Gem::Version.new(Facter.value(:powershell_version)) >= Gem::Version.new('5.0.10240.16384'))
+  confine :feature => :dsc_lite
   defaultfor :operatingsystem => :windows
 
   mk_resource_methods