This reverts commit fe14b2e5.

Reason for revert: failing test is reworked not to run angle_unittests
itself, but another binary.

Previously, this test was calling angle_unittests itself, but with a
different target.  On the bots, that was in turn calling angle_unittests
with even more arguments, including the addition of a log file location.
Under some configurations, this separate process was thus trying to
access files that were already opened by the parent process, leading to
a test failure.

In this CL, a new helper executable is created for the sake of this
unittest.

> Revert "Add system util to execute app and retrieve its output"
>
> This reverts commit c63d9552.
>
> Reason for revert: Test fails on Win7
>
> Original change's description:
> > Add system util to execute app and retrieve its output
> >
> > This will be useful to run external applications, such as benchmarks,
> > and process their output.
> >
> > Bug: angleproject:3125
> > Change-Id: Ic13c69f2e034f4b47498fb2f299c62423c355c4a
> > Reviewed-on: https://chromium-review.googlesource.com/c/1452534
> > Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
> > Reviewed-by: Jamie Madill <jmadill@google.com>

Bug: angleproject:3125, angleproject:3168
Change-Id: I74815750484a79f33c36e0b4f941d4dd98f99aa5
Reviewed-on: https://chromium-review.googlesource.com/c/1487631
Commit-Queue: Shahbaz Youssefi <syoussefi@chromium.org>
Reviewed-by: Jamie Madill <jmadill@google.com>
Reviewed-by: Yuly Novikov <ynovikov@chromium.org>