scripts/contrib/build-perf-test.sh: add a script for build performance tracking

scripts/contrib/build-perf-test.sh: add a script for build performance tracking

This script runs a series of builds (core-image-sato by default) with
and without sstate cache and collects some metrics (time and size currently).
It takes a commit as argument  (-c <rev>) and measures wall clock for
bitbake core-image-sato and virtual/kernel.

(From OE-Core rev: ee9538081a0bccfb7eb2888b1b51fe9b71c8cb81)

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