linux_aura: Reenable parallel_jobs_

linux_aura: Reenable parallel_jobs_.

In r239536 and r239680, I disabled all parallelization of unit test
jobs on linux_aura, because using the clipboard used a desktop wide
piece of X11 state, and running the tests in parallel meant that
tests which were using the clipboard would steal the clipboard from
other tests

The "actual" "problem" seems to have been "fixed." These tests appear
to be flakily failing in the same way in the GTK port, but are retried.
On lniux_aura, the test harness wasn't rerunning the tests and was just
marking them as failed. Now it's rerunning them, and they pass since
flaky tests are rerun one at a time.

This should still be a net win speed wise, since things fail flakily
about one in four times, and even that one flaky run still runs twice
as fast as the current runs.

BUG=239536
R=kbr@chromium.org, phajdan.jr@chromium.org

Committed: https://src.chromium.org/viewvc/chrome?view=rev&revision=243674

[Elliot Glaysher, 2014-01-07 21:49:12]

Yay. It's "fixed".

[Ken Russell (switch to Gerrit), 2014-01-07 21:53:36]

LGTM

This is great. The try job failures look unrelated, yes?

[Paweł Hajdan Jr., 2014-01-08 13:50:51]

LGTM

[commit-bot: I haz the power, 2014-01-08 19:03:43]

CQ is trying da patch. Follow status at
https://chromium-status.appspot.com/cq/erg@chromium.org/125183005/1

[Elliot Glaysher, 2014-01-08 22:25:17]

Committed patchset #1 manually as r243674 (presubmit successful).