run-tests: allow option parser to be extended This patch moves the OptionParser population into its own function so consumers may modify the OptionParser before arguments are evaluated. This will allow consumers to add custom options, set different defaults, etc.

run-tests: use return values instead of sys.exit

run-tests: Pass arguments into argument parser Before, arguments were not passed into the optparse.OptionParser instance and were coming from sys.argv. This patch enables consumers to define the list of arguments to parse without having to adjust sys.argv.

bundle2: rename part to bundlepart We are going to introduce an `unbundlepart` dedicated to reading bundle. So we need to rename the one used to create bundle. Even if dedicated to creation, this is still used for unbundling until we get the new class.

bundle2: comment to clarify why the handler call is where it is The reason why it is here is not obvious. I'm the one who wrote it there in the first place and almost moved it 2 weeks later.

bundle2: use chunkbuffer for exchange.getbundle We can use `util.chunkbuffer` instead.