Add dummy capability to void host plugin for testing

plugins/hosts/void/cap/dummy.rb

@@ -0,0 +1,11 @@
+module VagrantPlugins
+  module HostVoid
+    module Cap
+      class Dummy
+        def self.dummy(ui, argument)
+          raise "got argument: #{ui.inspect} and #{argument.inspect}"
+        end
+      end
+    end
+  end
+end

plugins/hosts/void/plugin.rb

@@ -25,6 +25,11 @@ module VagrantPlugins
         require_relative "cap/nfs"
         Cap::NFS
       end
+
+      host_capability("void", "dummy") do
+        require_relative "cap/dummy"
+        Cap::Dummy
+      end
     end
   end
 end