CI: pin python-dateutil for py2

Their 2.9.0 release is known-broken for py27-py35.

Change-Id: I40c1724fa673ac252f5052ac85006788ba69d5c7

lower-constraints.txt

@@ -79,3 +79,4 @@ voluptuous==0.11.1
 wrapt==1.10.11
 xattr==0.4
 pycadf===2.10.0
+python-dateutil===2.4.2

py2-constraints.txt

@@ -68,6 +68,10 @@ gitdb===0.6.4
 gitdb2===2.0.6
 pathlib2==2.3.6
 
+# python-dateutil seems likely to bring back support, but 2.9.0 is known-broken
+# see https://github.com/dateutil/dateutil/issues/1344
+python-dateutil===2.8.2
+
 # Projects that are known to have had a final py2-supporting release
 bandit===1.6.2
 python-keystoneclient===3.22.0

tools/playbooks/common/install_dependencies.yaml

@@ -53,8 +53,9 @@
     - name: install PasteDeploy - CentOS 7
       pip: name={{ item }} state=present extra_args='--upgrade'
       with_items:
-        # py2_constraints isn't obeyed by pip install swift
+        # py2_constraints won't be obeyed by pip install swift
         - 'PasteDeploy==2.1.1'
+        - 'python-dateutil==2.8.2'
       when:
         - ansible_facts['distribution'] == "CentOS"
         - ansible_facts['distribution_major_version'] == "7"