CI: Fix "error: externally-managed-environment"

Seems like the CI OS changed and now it won't allow installing Python
packages in the system without explicitly requesting that. This commit
solves this by installing needed packages through `apt-get`.

tests/ci-occm-e2e.sh

@@ -44,7 +44,8 @@ cleanup() {
 }
 trap cleanup EXIT
 
-python3 -m pip install requests ansible
+apt-get update
+apt-get install -y python3-requests ansible
 
 # If BOSKOS_HOST is set then acquire a resource of type ${RESOURCE_TYPE} from Boskos.
 if [ -n "${BOSKOS_HOST:-}" ]; then