Update some constraints for py2

We've recently started seeing some failures in the gate related to these
projects, and they have final py2-supporting versions.

Change-Id: If81fc352c8b2b1f03f3fa7b79c56dfcf981ced70

lower-constraints.txt

@@ -78,3 +78,4 @@ urllib3==1.22
 voluptuous==0.11.1
 wrapt==1.10.11
 xattr==0.4
+pycadf===2.10.0

py2-constraints.txt

@@ -73,3 +73,6 @@ gitdb2===2.0.6
 # Projects that are known to have had a final py2-supporting release
 bandit===1.6.2
 python-keystoneclient===3.22.0
+dnspython===1.16.0
+setuptools===44.1.1
+pycadf===2.10.0

tools/playbooks/common/install_dependencies.yaml

@@ -40,4 +40,6 @@
         - nose
         - pyeclib
         - python-swiftclient
-        - mock
+        # For some reason, pip on py2 isn't smart enough to prevent us
+        # trying to install a too-new mock??
+        - 'mock<4'