message: log_files: save files locally instead
  This removes the warning about tmpnam that I get at linking, and it
  means I can actually see and check the files that I downloaded.
diff: @@ -37,14 +37,15 @@ TEST(HardwareTest, LogFiles)
  LogInfo() << "Entry " << entry.id << ": "
  << " at " << entry.date << ", " << size_mib
  << " MiB, bytes: " << entry.size_bytes;
  - std::string file_path = std::tmpnam(nullptr);
  + std::stringstream file_path_stream;
  + file_path_stream << "./logfile_" << entry.id << ".ulog";
  auto prom = std::promise<void>();
  auto fut = prom.get_future();
  log_files->download_log_file_async(
  entry,
  - file_path,
  + file_path_stream.str(),
  [&prom](LogFiles::Result result, LogFiles::ProgressData progress_data) {
  if (result == LogFiles::Result::Next) {
  LogInfo() << "Download progress: " << 100.0f * progress_data.progress;
  @@ -92,14 +93,15 @@ TEST(HardwareTest, LogFilesDownloadFailsIfPathIsDirectory)
  << " at " << entry.date << ", " << size_mib
  << " MiB, bytes: " << entry.size_bytes;
  - std::string file_path = std::tmpnam(nullptr);
  + std::stringstream file_path_stream;
  + file_path_stream << "./logfile_" << entry.id << ".ulog";
  auto prom = std::promise<void>();
  auto fut = prom.get_future();
  log_files->download_log_file_async(
  entry,
  - file_path,
  + file_path_stream.str(),
  [&prom](LogFiles::Result result, LogFiles::ProgressData progress_data) {
  if (result == LogFiles::Result::Next) {
  LogInfo() << "Download progress: " << 100.0f * progress_data.progress;
  @@ -146,9 +148,10 @@ TEST(HardwareTest, LogFilesDownloadFailsIfFileAlreadyExists)
  LogInfo() << "Entry " << entry.id << ": "
  << " at " << entry.date << ", " << size_mib
  << " MiB, bytes: " << entry.size_bytes;
  - std::string file_path = std::tmpnam(nullptr);
  + std::stringstream file_path_stream;
  + file_path_stream << "./logfile_" << entry.id << ".ulog";
  - std::ofstream ofs(file_path);
  + std::ofstream ofs(file_path_stream.str());
  ofs << "This file should not be erased by the download\n";
  ofs.close();
  @@ -157,7 +160,7 @@ TEST(HardwareTest, LogFilesDownloadFailsIfFileAlreadyExists)
  log_files->download_log_file_async(
  entry,
  - file_path,
  + file_path_stream.str(),
  [&prom](LogFiles::Result result, LogFiles::ProgressData progress_data) {
  if (result == LogFiles::Result::Next) {
  LogInfo() << "Download progress: " << 100.0f * progress_data.progress;
  