(CAT-1869) - Add configurable dsc_timeout

This commit introduces a new instance variable @timeout, set
to nil by default. A new method set_dsc_timeout is added to
handle the setting of @timeout based on the name_hash[:dsc_timeout]
value. This timeout specifies the number of seconds the ps_manager will
await the dsc invocation to return, before moving on.

The ps_manager.execute method call now includes the timeout value.
The error message for when output is nil has been updated to include
information about the timeout, if it is set.

Does not affect previous behaviour, therefore is completely backwards
compatible with previous versions.

lib/puppet/provider/dsc_base_provider/dsc_base_provider.rb

@@ -15,6 +15,7 @@ def initialize
     @cached_query_results = []
     @cached_test_results = []
     @logon_failures = []
+    @timeout = nil # default timeout, ps_manager.execute is expecting nil by default..
     super
   end
 
@@ -251,13 +252,17 @@ def invoke_dsc_resource(context, name_hash, props, method)
       context.err('Logon credentials are invalid')
       return nil
     end
+    specify_dsc_timeout(name_hash)
     resource = invocable_resource(props, context, method)
     script_content = ps_script_content(resource)
+    context.debug("Invoke-DSC Timeout: #{@timeout} milliseconds") if @timeout
     context.debug("Script:\n #{redact_secrets(script_content)}")
-    output = ps_manager.execute(remove_secret_identifiers(script_content))[:stdout]
+    output = ps_manager.execute(remove_secret_identifiers(script_content), @timeout)[:stdout]
 
     if output.nil?
-      context.err('Nothing returned')
+      message = 'Nothing returned.'
+      message += " There is a timeout of #{@timeout} milliseconds set, ensure the DSC resource has enough time to apply." unless @timeout.nil?
+      context.err(message)
       return nil
     end
 
@@ -295,6 +300,18 @@ def invoke_dsc_resource(context, name_hash, props, method)
     data
   end
 
+  # Sets the @timeout instance variable.
+  # @param name_hash [Hash] the hash of namevars to be passed as properties to `Invoke-DscResource`
+  # The @timeout variable is set to the value of name_hash[:dsc_timeout] in milliseconds
+  # If name_hash[:dsc_timeout] is nil, @timeout is not changed.
+  # If @timeout is already set to a value other than nil,
+  # it is changed only if it's different from name_hash[:dsc_timeout]..
+  def specify_dsc_timeout(name_hash)
+    return unless name_hash[:dsc_timeout] && (@timeout.nil? || @timeout != name_hash[:dsc_timeout])
+
+    @timeout = name_hash[:dsc_timeout] * 1000
+  end
+
   # Retries Invoke-DscResource when returned error matches error regex supplied as param.
   # @param context [Object] the Puppet runtime context to operate in and send feedback to
   # @param max_retry_count [Int] max number of times to retry Invoke-DscResource