fix(build_packages): Remove unnecessary version info export.

Nothing in build_packages references the variables from
coreos_version.sh and nothing in our ebuilds depends on it being in the
environments so just remove it.
fix(scripts): Cleanup build version handling.

A few things here:
 - Source manifests/version.txt directly instead of coreos-version.sh
 - Remove Chrome branch from target image directory names.
 - Use proper version instead of timestap for catalyst builds.
 - Move lsb_release script from coreos-overlay to build_library.
Merge pull request #15 from marineam/version

Version handling cleanup