[test] Remove default for zero test cases.

[test] Remove default for zero test cases.

BUG=

Committed: https://crrev.com/4d6f1abbdb48b5f5ea00af120456d35db7553993
Cr-Commit-Position: refs/heads/master@{#28654}

[Michael Achenbach, 2015-05-26 19:45:28]

machenbach@chromium.org changed reviewers:
+ jkummerow@chromium.org

[Michael Achenbach, 2015-05-26 19:45:28]

PTAL. Any reason why that is needed? I'd like to remove it to always enforce
json output on the bots.

[Jakob Kummerow, 2015-05-27 08:28:46]

Here's a reason; this happens when I apply this patch:

$ tools/run-tests.py --arch x64 --mode release nonexistent
[...snip...]
>>> Running tests for x64.release
No connection to distribution server; running tests locally.
Traceback (most recent call last):
  File "tools/run-tests.py", line 655, in <module>
    sys.exit(Main())
  File "tools/run-tests.py", line 502, in Main
    code = Execute(arch, mode, args, options, suites, workspace)
  File "tools/run-tests.py", line 646, in Execute
    exit_code = runner.Run(options.j)
  File "...v8/tools/testrunner/local/execution.py", line 207, in Run
    self.indicator.Done()
  File "...v8/tools/testrunner/local/progress.py", line 170, in Done
    self.PrintProgress('Done')
  File "...v8/tools/testrunner/local/progress.py", line 205, in PrintProgress
    self.runner.total),
ZeroDivisionError: integer division or modulo by zero

Clearly, printing "No tests to run" looks much cleaner than a random exception,
and is much easier to get right than hardening all the other code to handle the
zero corner case correctly.

[Michael Achenbach, 2015-05-27 09:27:24]

How about this fix? I found only this one corner case. The alternative would be
to add some (ugly) extra code in the 0-test-cases case that prints the empty
json output.

[Jakob Kummerow, 2015-05-27 10:49:54]

OK, LGTM.

[Michael Achenbach, 2015-05-27 13:26:38]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-05-27 13:26:43]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1153103003/40001

[commit-bot: I haz the power, 2015-05-27 13:50:47]

Committed patchset #3 (id:40001)

[commit-bot: I haz the power, 2015-05-27 13:50:59]

Patchset 3 (id:??) landed as
https://crrev.com/4d6f1abbdb48b5f5ea00af120456d35db7553993
Cr-Commit-Position: refs/heads/master@{#28654}