Support for concurrency and rate limiting has been added to keystoneauth,
which is the library openstacksdk uses to talk to OpenStack. Instead
of managing concurrency in nodepool using the TaskManager and pool of
worker threads, let keystoneauth take over. This also means we no longer
have a hook into the request process, so we defer statsd reporting to
the openstacksdk layer as well.
Change-Id: If21a10c56f43a121d30aa802f2c89d31df97f121
Monty Taylor