Comment 7 for bug 1724623

Upstream merge request for parsing /etc/cloud/build.info: https://github.com/canonical/apport/pull/50

Please review https://github.com/canonical/apport/pull/50/commits/76e0f3475074a44fddd9e299489a1c32a811ba9d and let me know if you are happy with _BUILD_INFO_KEY_MAPPING or if there are better names.