Revert "Switch to futurist for concurrency"

This partially reverts commit b6a22e3749.

The addition of futurist as a hard depend broke python2, and at the
same time didn't mark the release as having done so. In looking at the
issue we realized that we don't actually need the hard depend.

Change-Id: I2d874f618f5b3f66d49cd2e964c6e05655f22c0f

.zuul.yaml

@@ -413,7 +413,6 @@
             voting: false
         - osc-functional-devstack-tips:
             voting: false
-        - nodepool-functional-openstack-src
         # Ironic jobs, non-voting to avoid tight coupling
         - ironic-inspector-tempest-openstacksdk-src:
             voting: false
@@ -428,4 +427,3 @@
         - openstacksdk-functional-devstack
         - openstacksdk-functional-devstack-networking
         - openstacksdk-functional-devstack-senlin
-        - nodepool-functional-openstack-src

lower-constraints.txt

@@ -9,7 +9,6 @@ extras==1.0.0
 fixtures==3.0.0
 future==0.16.0
 futures==3.0.0
-futurist==2.1.0
 ipaddress==1.0.17
 iso8601==0.1.11
 jmespath==0.9.0

openstack/connection.py

@@ -179,7 +179,7 @@ Additional information about the services can be found in the
 import warnings
 import weakref
 
-import futurist
+import concurrent.futures
 import keystoneauth1.exceptions
 import requestsexceptions
 import six
@@ -504,7 +504,7 @@ class Connection(
     @property
     def _pool_executor(self):
         if not self.__pool_executor:
-            self.__pool_executor = futurist.ThreadPoolExecutor(
+            self.__pool_executor = concurrent.futures.ThreadPoolExecutor(
                 max_workers=5)
         return self.__pool_executor
 

releasenotes/notes/revert-futurist-34acc42fd3f0e7f3.yaml

@@ -0,0 +1,8 @@
+---
+upgrade:
+  - |
+    Removed the dependency on futurist, which isn't necessary.
+    Users can still pass futurist executors if they want, as
+    the API is the same, but if nothing is passed,
+    ``concurrent.futures.ThreadPoolExecutor`` will be used as
+    the default.

requirements.txt

@@ -14,7 +14,7 @@ munch>=2.1.0 # MIT
 decorator>=4.4.1 # BSD
 jmespath>=0.9.0 # MIT
 ipaddress>=1.0.17;python_version<'3.3' # PSF
-futurist>=2.1.0 # Apache-2.0
+futures>=3.0.0;python_version=='2.7' or python_version=='2.6' # BSD
 iso8601>=0.1.11 # MIT
 netifaces>=0.10.4 # MIT