Removed cloudfiles dependency in SwiftFileBackend

* Added a new curl multi wrapper under libs/.
* Used the new MultiHttpClient class instead of CloudFiles
* Removed CDN related config and code as it does not work.
  well due to mutating files and tiny purge rate limits by CDNs.
* Also removed the unused and esoteric 'swiftAnonUser' parameter.
* Support concurrent 'describe' operations.
* Set ACLs on containers on intial PUT instead of in two steps.
  Previously if the second step failed, prepare() would never
  set the ACLs correctly since it aborts if the container exists.
* Improve token deletion to only trigger on 401s rather than other
  random errors like 50X timeouts.
* Removed duplicative getResponse* code by just using one closure
  called for both the concurrent and serial cases. Both cases are
  now funneled through doExecuteOpHandlesInternal().
* Add the MD5 to stat info, as it might be useful for speeding up
  the copy scripts in some cases (when both backends have md5 set).
* Avoid use of trigger_error() since there is a swift log group.
* A few other small code cleanups.

Change-Id: I1adb3e2df6df8cf01d3ad74158de96ea9a79da2e
Merge "Removed cloudfiles dependency in SwiftFileBackend"