auto-update test: wait for service to be ready

The symptoms in containers#17607 point to some race since it does not always flake
on Debian (and Debian only).  Hence, wait for the service to be ready
before building the image to make sure that the service is started with
the old image and that everything's in order.

Fixes: containers#17607
Signed-off-by: Valentin Rothberg <vrothberg@redhat.com>

test/system/255-auto-update.bats

@@ -239,11 +239,12 @@ function _confirm_update() {
 
 @test "podman auto-update - label io.containers.autoupdate=local" {
     generate_service localtest local
+    _wait_service_ready container-$cname.service
+
     image=quay.io/libpod/localtest:latest
     run_podman commit --change CMD=/bin/bash $cname $image
     run_podman image inspect --format "{{.ID}}" $image
 
-    _wait_service_ready container-$cname.service
     run_podman auto-update --dry-run --format "{{.Unit}},{{.Image}},{{.Updated}},{{.Policy}}"
     is "$output" ".*container-$cname.service,quay.io/libpod/localtest:latest,pending,local.*" "Image update is pending."