Updated openstack/openstack
Project: openstack/taskflow  45427dce0eee3762c6ef019547f31dfe9718a58a

Make greenexecutor not keep greenthreads active

Instead of keeping all greenthreads active even
if they are not being used only keep the greenthreads
active if there exists active work to complete.

This saves resources (each greenthread takes up
memory) and allows a pool to shrink and grow in
a more dynamic fashion.

Fixes bug 1339406

Change-Id: Idc8ab8447045915a0ffbaf21fa5c4bdb7a9e3593