swift: add swift-dispersion-report and stats

dispersion is a swift facility to assess the cluster health by writing
containers and objects across the cluster once and subsequently verify where
they are. http://docs.openstack.org/developer/swift/admin_guide.html

add a swift dispersion account plus the reporting wrapper around
swift-dispersion-report to push statistics to graphite (run by cron)

dispersion needs to be primed (once, per cluster) via
swift-dispersion-populate, this will be run upon cluster initialization
manually.

Change-Id: Icc323aa7103c8dca7c1ef5a407844523db8f5a09
Merge "swift: add swift-dispersion-report and stats" into production