CI: Install simplejson in swift scenario

Change-Id: I2145160a1e359988e519113400e8cd2c2a0b057e

roles/openstack-clients/defaults/main.yml

@@ -20,6 +20,10 @@ openstack_clients_pip_packages:
     enabled: "{{ scenario in ['octavia', 'ovn'] }}"
   - package: python-openstackclient
     enabled: true
+    # python-openstackclient 6.6.0 didn't work with swift due to https://review.opendev.org/c/openstack/python-openstackclient/+/920001
+    # TODO: remove the simplejson once new package released on pypi.org.
+  - package: simplejson
+    enabled: "{{ scenario == 'swift' }}"
   - package: python-tackerclient
     enabled: "{{ scenario == 'scenario_nfv' }}"
   - package: python-troveclient