Reset internal environment after plugin load

Force the vagrantfile and configuration loader to be rebuilt after
plugins have been loaded to properly allow newly introduced plugin
configurations to be properly supported within the Vagrantfile.

lib/vagrant/environment.rb

@@ -178,6 +178,10 @@ module Vagrant
       plugins = Vagrant::Plugin::Manager.instance.globalize!
       Vagrant::Plugin::Manager.instance.load_plugins(plugins)
 
+      # Reset so Vagrantfile will be reloaded with expected support for
+      # any new plugins provided
+      post_plugins_reset!
+
       # Call the hooks that does not require configurations to be loaded
       # by using a "clean" action runner
       hook(:environment_plugins_loaded, runner: Action::Runner.new(env: self))
@@ -913,6 +917,18 @@ module Vagrant
 
     protected
 
+    # Unsets the internal vagrantfile and config_loader
+    # to force them to be regenerated. This is used after
+    # plugins have been loaded so that newly discovered
+    # plugin configurations are properly available
+    #
+    # @return [nil]
+    def post_plugins_reset!
+      @vagrantfile = nil
+      @config_loader = nil
+      nil
+    end
+
     # Check for any local plugins defined within the Vagrantfile. If
     # found, validate they are available. If they are not available,
     # request to install them, or raise an exception

test/unit/vagrant/environment_test.rb

@@ -25,6 +25,13 @@ describe Vagrant::Environment do
   let(:instance)  { env.create_vagrant_env }
   subject { instance }
 
+  describe "#initialize" do
+    it "should do an internal reset after plugin loading" do
+      expect_any_instance_of(described_class).to receive(:post_plugins_reset!)
+      instance
+    end
+  end
+
   describe "#can_install_provider?" do
     let(:plugin_hosts) { {} }
     let(:plugin_host_caps) { {} }