[tools/perf] Fix run_benchmark return code

The CL introducing the results processor [1] broke reporting of
Telemetry's return_code when called via run_benchmark.

[1]: https://chromium-review.googlesource.com/c/chromium/src/+/1692986

This is a quick fix for that.

Adding tests to make sure we don't break this again in the future as
follow up CLs.

TBR=crouleau@chromium.org

Bug: 990472
Change-Id: I4139d4b7503bad6555b5ee8d919499dd32fbff37
Reviewed-on: https://chromium-review.googlesource.com/c/chromium/src/+/1735581Reviewed-by: Juan Antonio Navarro Pérez <perezju@chromium.org>
Commit-Queue: Juan Antonio Navarro Pérez <perezju@chromium.org>
Cr-Commit-Position: refs/heads/master@{#683972}

tools/perf/core/benchmark_runner.py

@@ -19,5 +19,6 @@ def main(config):
       environment=config,
       results_arg_parser=results_processor.ArgumentParser())
   results_processor.ProcessOptions(options)
-  command_line.RunCommand(options)
-  results_processor.ProcessResults(options)
+  run_return_code = command_line.RunCommand(options)
+  process_return_code = results_processor.ProcessResults(options)
+  return max(run_return_code, process_return_code)

tools/perf/core/results_processor/processor.py

@@ -111,6 +111,6 @@ def ProcessResults(options):
       after any adjustments from ProcessOptions were applied.
   """
   if not getattr(options, 'output_formats', None):
-    return
+    return 0
 
   raise NotImplementedError(options.output_formats)