Code review comment for lp:~pundiramit/linaro-android-build-tools/access_private_manifests

Ok, I tested a few cases (based on galaxynexus-linaro build):

 1. SOURCE_OVERLAY missing, SOURCE_OVERLAY_OPTIONAL=1
    https://android-build.linaro.org/jenkins/job/danilo_optional-overlay/1/console

    Ok, fails with SOURCE_OVERLAY missing.

 2. SOURCE_OVERLAY present, SOURCE_OVERLAY_OPTIONAL=1
    https://android-build.linaro.org/jenkins/job/danilo_optional-overlay/2/console

    OK, fails with your new error message.

 3. SOURCE_OVERLAY present, no SOURCE_OVERLAY_OPTIONAL (regular builds)
    https://android-build.linaro.org/jenkins/job/danilo_optional-overlay/3/console

    Just starting now. If that one builds ok, I'll merge your branch asap.