Add no-op mode, profiling, msgpack vs. yaml, sped up ssbench-master

Added --noop option for ssbench-master which just passes work jobs to
the worker(s) which do nothing.  This lets you see the theoretical max
requests per second throughput without involving any requests to a Swift
cluster.  Fixes #11.

Added ability to profile master and worker.  Fixes #12.

Replaced yaml serialization with msgpack.  Unsurprisingly, msgpack is
much faster than yaml.  Fixes #5.

Got rid of some "non-blocking result sinking" code which was really
slowing down ssbench-master without adding any benefit.