scripts/contrib/build-perf-test.sh: add branch name and sizes to results

Be more descriptive about the revision we are running on
in the global results file: add branch:commit and git describe fields.
Also add the sizes for tmp dir not only times. (previously these were
only available in the output.log)

Signed-off-by: Stefan Stanacar <stefanx.stanacar@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>
scripts/contrib/build-perf-test.sh: fix passing arguments

Don't pass arguments to bitbake as a single one,
because this will break when the bitbake double-exec
is removed.

Signed-off-by: Stefan Stanacar <stefanx.stanacar@intel.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>