fix provisioner issue in vagrant 1.5

relates to #80

lib/vagrant-hostmanager/plugin.rb

@@ -29,6 +29,12 @@ module VagrantPlugins
         Provisioner
       end
 
+      # Work-around for vagrant >= 1.5
+      # It breaks without a provisioner config, so we provide a dummy one
+      config(:hostmanager, :provisioner) do
+        ::Vagrant::Config::V2::DummyConfig.new
+      end
+
       command(:hostmanager) do
         require_relative 'command'
         Command

test/Vagrantfile

@@ -22,4 +22,10 @@ Vagrant.configure('2') do |config|
     server.vm.hostname = 'bender'
     server.vm.network :private_network, :ip => '10.0.5.3'
   end
-end
+
+  config.vm.define :server3 do |server|
+    server.vm.hostname = 'leena'
+    server.vm.network :private_network, :ip => '10.0.5.4'
+    server.vm.provision :hostmanager
+  end
+end