oe-build-perf-report: Improve branch comparision handling
When comparing branches, correctly filter the revisions corresponding
to the specific branch specified.
Also use the commit numbers as a way to gauge spatially related commits
for comparision meaning comparisions for out of order build revisions
becomes meaninful.
This should improve the reporting for autobuilder generated builds.
Also improve the branch option help text.
(From OE-Core rev:
9f6f4ab6eec9dca07af7f53da5f737a6167bfb38)
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
