provisioner/remote-exec: Move script cleanup after command wait

The script cleanup step added in #5577 was positioned before the
`cmd.Wait()` call to ensure the command completes. This was causing
non-deterministic failures, especially for longer running scripts.

Fixes #5699
Fixes #5737

builtin/provisioners/remote-exec/resource_provisioner.go

@@ -176,8 +176,8 @@ func (p *ResourceProvisioner) runScripts(
  go p.copyOutput(o, outR, outDoneCh)
  go p.copyOutput(o, errR, errDoneCh)
 
+ remotePath := comm.ScriptPath()
  err = retryFunc(comm.Timeout(), func() error {
- remotePath := comm.ScriptPath()
 
  if err := comm.UploadScript(remotePath, script); err != nil {
  return fmt.Errorf("Failed to upload script: %v", err)
@@ -192,13 +192,6 @@ func (p *ResourceProvisioner) runScripts(
  return fmt.Errorf("Error starting script: %v", err)
  }
 
- // Upload a blank follow up file in the same path to prevent residual
- // script contents from remaining on remote machine
- empty := bytes.NewReader([]byte(""))
- if err := comm.Upload(remotePath, empty); err != nil {
- return fmt.Errorf("Failed to upload empty follow up script: %v", err)
- }
-
  return nil
  })
  if err == nil {
@@ -214,6 +207,14 @@ func (p *ResourceProvisioner) runScripts(
  <-outDoneCh
  <-errDoneCh
 
+ // Upload a blank follow up file in the same path to prevent residual
+ // script contents from remaining on remote machine
+ empty := bytes.NewReader([]byte(""))
+ if err := comm.Upload(remotePath, empty); err != nil {
+ // This feature is best-effort.
+ log.Printf("[WARN] Failed to upload empty follow up script: %v", err)
+ }
+
  // If we have an error, return it out now that we've cleaned up
  if err != nil {
  return err