Ssbench

* Fix 123: ssbench should detect closed connections and not reuse them.

* Fix 124: update the README instructions for using ssbench with
* virtualenv.

* Fix 117: ssbench cleanup-containers needs to be aware of the policy
suffix (otherwise no containers are cleaned up).

* Fix 96: when reporting average time per request, if no time elapsed
(happens if --noop was specified), ssbench should not print a
DivideByZero exception. The behavior is changed to print "inf" in such
cases.

* Added IPv6 support for the master and workers.

* Added errors, retries and retry_rate to cvs output.

* Removed the statlib dependency.

* Updated README to encourage using virtualenv.

* Updated AUHORS file.

* Misc test fixes/improvements including Travis CI integration.

* Improved Python 2.6 support.

* Fixed bug in batch job generation when job decoration fails.

* Worker job exceptions no longer count toward request counts.

* Updated AUTHORS file.

* Always print the distribution of requests per worker-ID in the report.

* Allow ssbench-master to override the default work block size used for
GET/PUT operations (-b BYTES or --block-size BYTES)

* Document the container_base key in the scenario file and allow a
non-default value for that to be passed into the cleanup-containers
sub-command.

* Updated AUTHORS file (sorry guys!)

* Fixed 66: Add cleanup-containers command to ssbench-master to delete all
ssbench-created containers and objects.

* Fixed 65: Only create initial files if they're not already present (try
to HEAD them first)

* Pick a storage URL for each request (better multiple -S support)

* Lowered default ssbench-worker concurrency level to 64