Bring in a newer optional eventlet

Since the openstack requirements repo just accepted eventlet>=0.15.1
we might as well also use that version in our optional requirements
and remove a piece of code that was dealing with a bug that was fixed
in eventlet 0.15.

Change-Id: I9b4f9061c7adb7d72315315f41bb0d742b6f56b5

taskflow/utils/eventlet_utils.py

@@ -144,9 +144,7 @@ class GreenExecutor(futures.Executor):
             self._shutdown = True
         if wait:
             self._pool.waitall()
-            # NOTE(harlowja): Fixed in eventlet 0.15 (remove when able to use)
-            if not self._delayed_work.empty():
-                self._delayed_work.join()
+            self._delayed_work.join()
 
 
 class _GreenWaiter(object):

tox.ini

@@ -61,14 +61,14 @@ basepython = python2.6
 deps = {[testenv]deps}
     -r{toxinidir}/requirements-py2.txt
     MySQL-python
-    eventlet>=0.13.0
+    eventlet>=0.15.1
     SQLAlchemy>=0.7.8,<=0.7.99
 
 [testenv:py27]
 deps = {[testenv]deps}
     -r{toxinidir}/requirements-py2.txt
     MySQL-python
-    eventlet>=0.13.0
+    eventlet>=0.15.1
     SQLAlchemy>=0.7.8,<=0.9.99
     doc8
 commands =