Add more command-line options to swift-bench.

These settings:
  1. are already exposed via config file
  2. were not exposed as command-line options, and
  3. are things I wanted on the command line while benchmarking recently.

I didn't include short options for --(get|put|delete)-concurrency
since I couldn't think of good single-letter ones, and optparse won't
take "-gc", "-pc", or "-dc".

Change-Id: I0bd7c7ae2892244eed37b8c10c9357dc7e1190d3
Merge "Add more command-line options to swift-bench."
Add handler for CORS "actual requests"

Fix for bug 1095130

* Added a wrapper function around public methods to handle
  CORS actual requests. These requests need to return some
  extra headers to be valid responses to a CORS request.
  Access-Control-Expose-Headers and Access-Control-Allow-Origin.

* Added support for the CORS header Access-Control-Expose-Headers.

* Some refactoring of the OPTIONS method so the
  "is_origin_allowed" logic can be reused.

* Added a little extra detail to the CORS documentation.

DocImpact

Change-Id: I68538e472a900775427f21a8a59e738a83dcc8bc
Merge "Add handler for CORS "actual requests""