Add a requirements.txt to the ansible container and have pip install …

ansible-playbook/Dockerfile

@@ -1,5 +1,8 @@
 FROM python:3.7
 
+ADD requirements.txt /tmp/requirements.txt
+RUN pip install -r /tmp/requirements.txt
+
 RUN pip install 'ansible~=$ANSIBLE_VERSION'
 
 ENV VAULT_PASSWORD=

ansible-playbook/requirements.txt

@@ -0,0 +1,4 @@
+# Additional modules required to support provisioning OpenStack resources via
+# Ansible.
+openstacksdk
+netaddr