Wrap CleanOldDir warning with informative message

main.go

@@ -70,7 +70,7 @@ func main() {
  log.SetDefaultLogger()
  err := execMain()
  if cleanupErr := fileutils.CleanOldDirs(); cleanupErr != nil {
- clientlog.Warn(cleanupErr)
+ clientlog.Warn("failed while attempting to cleanup old CLI temp directories:", cleanupErr)
  }
  coreutils.ExitOnErr(err)
 }