Merge lp://qastaging/~pundiramit/linaro-android-build-tools/labt into lp://qastaging/linaro-android-build-tools

This is a bit confusing. We require SOURCE_OVERLAY to be set (this was a recent change, so that's perhaps why it feels like a regression), for BUILD-INFO.txt file to be generated. Otherwise, someone can circum-vent our protection mechanisms (and more likely, build results will simply be inaccessible).

Then, this branch also deals with access to private repositories, but I am not sure I understand exactly what's going on. Can you please clarify the rationale for the changes?

Making SOURCE_OVERLAY optional is a requirement from Android platform team and yes we may have overlooked certain things which you pointed out. I'll get back to you on this in a while.

Meanwhile I'll upload "access to private manifest repositories" changes to a new branch.

Ok, I've discussed this with Vishal: the goal of this is to enable produced linaro_android_build_cmds.sh to work without the SOURCE_OVERLAY when not really needed. Since we do not use this script for actually building Android on jenkins, it's ok if this script has an override for SOURCE_OVERLAY (eg. perhaps set it to SOURCE_OVERLAY=ignore; if you want to do it any other way, that's fine as well).

However, the actual jenkins build should not allow that to be set in the build config (on android-build.linaro.org).