core: just don't use ** to avoid symbol/strings mixup

/cc @sethvargo

lib/vagrant/machine.rb

@@ -150,9 +150,11 @@ module Vagrant
     # @param [Hash] extra_env This data will be passed into the action runner
     #   as extra data set on the environment hash for the middleware
     #   runner.
-    def action(name, **opts)
+    def action(name, opts=nil)
       @logger.info("Calling action: #{name} on provider #{@provider}")
 
+      opts ||= {}
+
       # Determine whether we lock or not
       lock = true
       lock = opts.delete(:lock) if opts.has_key?(:lock)

test/unit/vagrant/machine_test.rb

@@ -252,13 +252,24 @@ describe Vagrant::Machine do
       expect(machine).to eql(instance)
     end
 
+    it "should pass any extra options to the environment" do
+      action_name = :up
+      foo         = nil
+      callable    = lambda { |env| foo = env[:foo] }
+
+      allow(provider).to receive(:action).with(action_name).and_return(callable)
+      instance.action(:up, foo: :bar)
+
+      expect(foo).to eq(:bar)
+    end
+
     it "should pass any extra options to the environment as strings" do
       action_name = :up
       foo         = nil
       callable    = lambda { |env| foo = env["foo"] }
 
       allow(provider).to receive(:action).with(action_name).and_return(callable)
-      instance.action(:up, foo: :bar)
+      instance.action(:up, "foo" => :bar)
 
       expect(foo).to eq(:bar)
     end