[#72115932] Update packaging to handle alternate Gemfile

 - Update jetpack from upstream and re-apply chorus additions. Now we can remove
   vendored bundler 1.1 and and the boot.rb $LOAD_PATH hack.
 - New hack in boot.rb for using the alternate Gemfile if it exists in production
   Binstubs (e.g. bin/rake) are created by bundler to properly reference the alternate
   Gemfile.
 - Update some usages of bin/rake to use bin/ruby -s bin/rake