Land rapid7#4226, user friendly Bundler error message

Fixes rapid7#4222, thanks @jhart-r7!

Author: Tod Beardsley

config/boot.rb

@@ -23,15 +23,13 @@
 end
 
 begin
-  require 'bundler'
+  require 'bundler/setup'
 rescue LoadError
   $stderr.puts "[*] Metasploit requires the Bundler gem to be installed"
   $stderr.puts "    $ gem install bundler"
-  exit(0)
+  exit(1)
 end
 
-Bundler.setup
-
 lib_path = root.join('lib').to_path
 
 unless $LOAD_PATH.include? lib_path