[swarming] Run unittests together with default tests.

[swarming] Run unittests together with default tests.

This adds the unittests to the "default" test set. Now that
the "default" and the DEFAULT_TESTS (i.e. runner with
no arguments) are the same, removed DEFAULT_TESTS and use
TEST_MAP["default"] instead.

On the bots, where unittests and default were run in
separation before, the explicit unittests step should now
be skipped.

This is necessary for swarming, as the unittests step is
too small to justify its own swarming job.

BUG=chromium:535160
LOG=n

Committed: https://crrev.com/35d2028d10668e69c1a71fb17b65eabbf2254982
Cr-Commit-Position: refs/heads/master@{#31122}

[Michael Achenbach, 2015-10-06 08:31:43]

The CQ bit was checked by machenbach@chromium.org to run a CQ dry run

[commit-bot: I haz the power, 2015-10-06 08:31:56]

Dry run: CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1374733006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1374733006/1

[Michael Achenbach, 2015-10-06 08:37:24]

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

[Michael Achenbach, 2015-10-06 08:37:25]

PTAL

[Benedikt Meurer, 2015-10-06 08:38:15]

LGTM (rubber-stamped)

[Michael Achenbach, 2015-10-06 09:04:16]

The CQ bit was unchecked by machenbach@chromium.org

[Michael Achenbach, 2015-10-06 09:04:19]

The CQ bit was checked by machenbach@chromium.org

[commit-bot: I haz the power, 2015-10-06 09:04:26]

CQ is trying da patch. Follow status at
 https://chromium-cq-status.appspot.com/patch-status/1374733006/1
View timeline at
 https://chromium-cq-status.appspot.com/patch-timeline/1374733006/1

[commit-bot: I haz the power, 2015-10-06 09:31:41]

Committed patchset #1 (id:1)

[commit-bot: I haz the power, 2015-10-06 09:31:57]

Patchset 1 (id:??) landed as
https://crrev.com/35d2028d10668e69c1a71fb17b65eabbf2254982
Cr-Commit-Position: refs/heads/master@{#31122}

[kjellander_chromium, 2015-10-06 10:07:23]

kjellander@chromium.org changed reviewers:
+ kjellander@chromium.org

[kjellander_chromium, 2015-10-06 10:07:24]

lgtm