Remove VAGRANT_DEBUG.

VAGRANT_LOG handles it all now.

bin/vagrant

@@ -31,9 +31,13 @@ begin
   # Kick start the CLI
   Vagrant::CLI.start(ARGV, :env => env)
 rescue Vagrant::Errors::VagrantError => e
+  logger.error("Vagrant experienced an error! Details:")
+  logger.error(e.inspect)
+  logger.error(e.message)
+  logger.error(e.backtrace.join("\n"))
+
   opts = { :prefix => false }
   env.ui.error e.message, opts if e.message
-  env.ui.error e.backtrace.join("\n"), opts if ENV["VAGRANT_DEBUG"]
   exit e.status_code if e.respond_to?(:status_code)
   exit 999 # An error occurred with no status code defined
 end