build-webos: Add WEBOS_DISTRO_BUILD_INFO to BB_ENV_EXTRAWHITE

Adding WEBOS_DISTRO_BUILD_INFO to BB_ENV_EXTRAWHITE makes it possible to
override it with environment variable

[GF-2461] Invent/create build variable with build-number and jenkins
job name

Open-webOS-DCO-1.0-Signed-off-by: Janne Hurskainen <janne.hurskainen@palm.com>