In some cases, gclient root is not the parent directory, it might be two
levels above.

This fixes it by asking gclient for the real root directory.

Bug: 760633
Change-Id: I82d754f1c53259a111a74628f784d1bc461c18ef
Reviewed-on: https://chromium-review.googlesource.com/999971Reviewed-by: Aaron Gable <agable@chromium.org>
Commit-Queue: Edward Lesmes <ehmaldonado@chromium.org>