function generalizeFilePath (filePath) {
  return filePath.replace(/^.*?\/build\//, '')
}
Takes an absolute, lambda file path (e.g., /var/task/build/sdks/android_2016-10-21_19-26Z.zip and generalizes it
into a relative path suitable for use as a static s3 site key (e.g., sdks/android_2016-10-21_19-26Z.zip).

@param {string} filePath
@returns {string} Relative file path, starting at (and excluding) the first occurrence of /build/