[core] Remove bundler usage for plugin management

bin/vagrant

@@ -45,18 +45,6 @@ argv.each_index do |i|
   end
 end
 
-# First, make sure that we're executing using the proper Bundler context
-# with our plugins. If we're not, then load that and reload Vagrant.
-if !ENV["VAGRANT_INTERNAL_BUNDLERIZED"]
-  require "rbconfig"
-  ruby_path = File.join(RbConfig::CONFIG["bindir"], RbConfig::CONFIG["ruby_install_name"])
-  Kernel.exec(
-    ruby_path,
-    File.expand_path("../../lib/vagrant/pre-rubygems.rb", __FILE__),
-    *ARGV)
-  raise "Fatal error: this line should never be reached"
-end
-
 # Set logging level to `debug`. This is done before loading 'vagrant', as it
 # sets up the logging system.
 if argv.include?("--debug")

lib/vagrant.rb

@@ -77,7 +77,6 @@
   global_logger.info("  - #{spec.name} = #{spec.version}")
 end
 
-
 # We need these components always so instead of an autoload we
 # just require them explicitly here.
 require "vagrant/plugin"
@@ -254,6 +253,11 @@ def self.original_env
   I18n.config.enforce_available_locales = true
 end
 
+# Setup the plugin manager and load any defined plugins
+require_relative "vagrant/plugin/manager"
+plugins = Vagrant::Plugin::Manager.instance.installed_plugins
+Vagrant::Bundler.instance.init!(plugins)
+
 # A lambda that knows how to load plugins from a single directory.
 plugin_load_proc = lambda do |directory|
   # We only care about directories