Header inclusion ordering style addition

[Patrick Venture]

On Tue, Aug 28, 2018 at 11:59 PM Tanous, Ed <ed.tanous at intel.com> wrote:
>
> I should also mention that bmcweb already uses the clang-format file to order headers based on some specific libraries.  It might be a decent example of how to do it for other repositories.
>
> https://github.com/openbmc/bmcweb/blob/master/.clang-format

In this gtest/gmock are put above the other headers, which I think
makes sense for the test code at least, I will grab this explicit line
and add it to the review in progress.

PTAL -- also, there is a review of this clang-format under the docs repo:

https://gerrit.openbmc-project.xyz/12180

>
> -Ed