Add tools/gate/build-images script

It will simplify configuring and tuning for our upcoming images
gating. In gate job we'll just exec this script and it will do
all the things we need. Let's start just with the building all
images for the specified plugin.

Change-Id: Iecef82bec8eb8d10218c5ad2b763ccabb41053ad
(cherry picked from commit 8f38712e1f62d3e0e7bb50133c029f57825dec2c)