This patch adds support for a new task executor. This executor
leverages the taskflow library which is responsible for dispatching
the tasks.
The taskflow executor provides basic serial execution of the
tasks and uses eventlet by default. The execution mode is configurable
to have parallel execution in which case it is possible to also
configure the number of workers running at the same time.
TaskFlow wiki: https://wiki.openstack.org/wiki/TaskFlow
partially implements bp async-glance-workers
partially implements bp taskflow-integration
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Co-Authored by: Arnaud Legendre <arnaudleg@gmail.com>
Co-Authored by: Flavio Percoco <flaper87@gmail.com>
Co-Authored by: Nikhil Komawar <nikhil.komawar@rackspace.com>
Change-Id: Ie31e64f8fee7f9fe7336cde50d5db89577c4f76d