Remove local provider injection to machine

plugins/commands/serve/service/provider_service.rb

@@ -58,18 +58,7 @@ module VagrantPlugins
             )
             options = Type::Options.new(value: {}) if options.nil?
 
-            provider = plugin.new(machine)
-
-            # Within Ruby, many actions are defined inside provider plugins,
-            # and within their implementations they assume that
-            # `machine.provider` yields an instance of their provider. A common
-            # instance of this assumption would be a call like
-            # `machine.provider.driver.some_implementation_specific_method`.
-            #
-            # Because these assumptions are rampant within the Ruby
-            # implementations of providers, we break encapsulation here to set
-            # the local copy of the provider plugin on the machine.
-            machine.instance_variable_set(:@provider, provider)
+            provider = load_provider(plugin, machine)
 
             callable = provider.action(action_name)
             if callable.nil?