[testrunner] Print relative test command

This makes the output a lot smaller and thus makes it easier to see the
relevant part of the command.

R=machenbach@chromium.org

Change-Id: I62ac7218be4a02f0270a2d88a2f69b6ced45a041
Reviewed-on: https://chromium-review.googlesource.com/c/1491597
Commit-Queue: Tamer Tas <tmrts@chromium.org>
Reviewed-by: Michael Achenbach <machenbach@chromium.org>
Reviewed-by: Tamer Tas <tmrts@chromium.org>
Cr-Commit-Position: refs/heads/master@{#59931}

tools/testrunner/testproc/progress.py

@@ -187,7 +187,7 @@ class CompactProgressIndicator(ProgressIndicator):
         print(self._templates['stdout'] % stdout)
       if len(stderr):
         print(self._templates['stderr'] % stderr)
-      print("Command: %s" % result.cmd)
+      print("Command: %s" % result.cmd.to_string(relative=True))
       if output.HasCrashed():
         print("exit code: %d" % output.exit_code)
         print("--- CRASHED ---")