Give ECAppIter greenthreads a chance to wrap up

Otherwise, we can hit a "generator already executing" error in
test/functional/test_slo.py:TestSlo.test_slo_multi_ranged_get

Also, set a *slightly* newer lower-bound for greenlet (from 2011 instead
of 2010) so the sleep() doesn't cause us to lose exception state.

Change-Id: Id458fc0a43fd71aab9f6edbacc1f0b370c9f7537

lower-constraints.txt

@@ -25,7 +25,7 @@ flake8==2.5.5
 future==0.16.0
 gitdb2==2.0.3
 GitPython==2.1.8
-greenlet==0.3.1
+greenlet==0.3.2
 hacking==0.11.0
 idna==2.6
 imagesize==1.0.0

requirements.txt

@@ -4,7 +4,7 @@
 
 dnspython>=1.15.0;python_version=='2.7' # http://www.dnspython.org/LICENSE
 eventlet>=0.25.0                        # MIT
-greenlet>=0.3.1
+greenlet>=0.3.2
 netifaces>=0.8,!=0.10.0,!=0.10.1
 PasteDeploy>=1.3.3
 lxml>=3.4.1

swift/proxy/controllers/obj.py

@@ -38,7 +38,7 @@ from hashlib import md5
 from swift import gettext_ as _
 
 from greenlet import GreenletExit
-from eventlet import GreenPile
+from eventlet import GreenPile, sleep
 from eventlet.queue import Queue
 from eventlet.timeout import Timeout
 
@@ -1066,6 +1066,7 @@ class ECAppIter(object):
         # executing the internal_parts_iters.
         if self.stashed_iter:
             self.stashed_iter.close()
+        sleep()  # Give the per-frag threads a chance to clean up
         for it in self.internal_parts_iters:
             close_if_possible(it)