Add ansible openstack collection

This requires at least ansible version 2.9. A new requirements file
is added to specify collections, and the env-prep script is modified
to install the openstack collection into the default collection
location.

Change-Id: I90b7ca4ea9491c3de197cbc4df83f7f959dd9571

test-ansible-collection-requirements.yml

@@ -0,0 +1,4 @@
+collections:
+  - name: openstack.cloud
+    version: 1.0.0
+    source: https://galaxy.ansible.com

test-ansible-env-prep.sh

@@ -211,6 +211,9 @@ fi
 # Install all python packages
 python -m pip install ${PIP_OPTS}
 
+# Install all ansible collections
+ansible-galaxy collection install -r ${COMMON_TESTS_PATH}/test-ansible-collection-requirements.yml
+
 # Download the Ansible role repositories if they are not present on the host.
 # This is ignored if there is no ansible-role-requirements file.
 if [[ ! -d "${ANSIBLE_ROLE_DEP_DIR}" ]]; then