Commit fast-build patch to portage_tool repository.

This patch allows us to selectively disable Portage locks in parallel_emerge.
It is not intended to be upstreamed but is left in for now until we find a way
to replace it (e.g. by integrating parallel emerge support directly into portage

Change-Id: I4ea50e206102b249ba01d2f760ebaba221bddd18

TEST=build_packages --nousepkg

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