Adding below features to packager
Packager to take os name and version
Packager to take a post script
Packager to proceed even if base_packages.cfg do not exists
Packager to display defaults
Packager to populate defaults

Change-Id: If25877e3a696d782045f66586aaf0d64bff7d76b
Merge "Adding below features to packager Packager to take os name and version Packager to take a post script Packager to proceed even if base_packages.cfg do not exists Packager to display defaults Packager to populate defaults"