fix(common.sh): Correctly report script name in tracebacks

Pretty simple typo.
fix(build_packages): Move gsutil code from build_packages to a library.

To avoid making the same gsutil changes in more scripts move the code to
a library file where some of the basic parts can be shared.
feat(build_image): Add upload support for official builds
fix(bootstrap_sdk): Report the time it took to complete
Merge pull request #23 from marineam/images

Upload official filesystem images