Don't output stdout and stderr twice when shell provisioner fails

[GH-4086]

plugins/provisioners/shell/provisioner.rb

@@ -65,7 +65,11 @@ module VagrantPlugins
             end
 
             # Execute it with sudo
-            comm.execute(command, sudo: config.privileged) do |type, data|
+            comm.execute(
+              command,
+              sudo: config.privileged,
+              error_key: :ssh_bad_exit_status_muted
+            ) do |type, data|
               handle_comm(type, data)
             end
           end

templates/locales/en.yml

@@ -968,6 +968,9 @@ en:
         Stderr from the command:
 
         %{stderr}
+      ssh_bad_exit_status_muted: |-
+        The SSH command responded with a non-zero exit status.
+        Vagrant assumes that this means the command failed!
       ssh_connect_eacces: |-
         SSH is getting permission denied errors when attempting to connect
         to the IP for SSH. This is usually caused by network rules and not being