message: When we use AWSSDK, bpls should not check if the file  it exists locally but should demand specifying the engine explicitly.
diff: @@ -1533,11 +1533,29 @@ int doList(const char *path)
  if (verbose > 1)
  printf("\nADIOS Open: read header info from %s\n", path);
  + std::string tpl = helper::LowerCase(transport_params);
  + bool remoteFile = (tpl.find("awssdk") != std::string::npos);
  + if (remoteFile)
  + {
  + if (engine_name.empty())
  + {
  + fprintf(
  + stderr,
  + "\nError: For remote file access you must specify the engine "
  + "explicitly with -E parameter, e.g. -E bp5 or -E bp4 or -E "
  + "bp3.\nVirtual engines like BPFile or FileStream do not know "
  + "which engine to use.\n");
  + return 8;
  + }
  + }
  + else
  + {
  if (!adios2sys::SystemTools::FileExists(path))
  {
  fprintf(stderr, "\nError: input path %s does not exist\n", path);
  return 4;
  }
  + }
  // initialize BP reader
  if (verbose > 1)
  