Print a message on log collection

This helps separate visually the cleanup stage from the "interesting"
part of the CI job output.

test-driver

@@ -53,6 +53,7 @@ save_logs() {
 
     # Try to keep ansible-playbook output to a minimum so as not to
     # take too much space in the CI job logs.
+    log "Saving logs from VMs (if any)"
     mkdir -p "${out_dir}"
     ANSIBLE_STDOUT_CALLBACK=null \
     ${float_dir}/float run --extra-vars "out_dir=${out_dir}" \