py2constraints: pin PasteDeploy version

PasteDeploy version 3.0 (2022-10-16) dropped support for python2 (as
well as <3.7), which causes our py2 tests to fail. So cap the version
here at 2.1.1, the last which is compatible with our tests.

Even doing this doesn't stop pip install swift pulling in a newer
PasteDeploy in the
tools/playbooks/saio_single_node_setup/make_rings.yaml playbook
(causing the probes test on CentOS-7 to fail); so handle CentOS 7
explicitly.

Change-Id: If69ae0f8eac8fe8ff7d5e4f4f1bff6d0ea9e7a8b
Signed-off-by: Matthew Vernon <mvernon@wikimedia.org>
(cherry picked from commit cc033154ad)
(cherry picked from commit d05ddb0364)

py2-constraints.txt

@@ -73,3 +73,4 @@ gitdb2===2.0.6
 
 # Projects that are known to have had a final py2-supporting release
 bandit===1.6.2
+PasteDeploy==2.1.1

tools/playbooks/common/install_dependencies.yaml

@@ -36,3 +36,12 @@
       with_items:
         - crudini
         - eventlet
+
+    - name: install PasteDeploy - CentOS 7
+      pip: name={{ item }} state=present extra_args='--upgrade'
+      with_items:
+        # py2_constraints isn't obeyed by pip install swift
+        - 'PasteDeploy==2.1.1'
+      when:
+        - ansible_facts['distribution'] == "CentOS"
+        - ansible_facts['distribution_major_version'] == "7"