test/system: speed up "podman auto-update using systemd"

Defining a timer with a fixed interval is not a good idea as we first
have to wait until the timer triggers, while the interval was every two
seconds it means that we have to wait at least 2s for it to start.
However much worse it means it triggers the unit over and over, this
seems to cause some soft of race with the output check. I have seen
this test run 10-60s which does not make much sense.

Switching the timer to trgger once on start seem to make the test run
consistently in 7s locally for me so this is much better.

There still is the question if we really have to test this at all on
each upstream PR but I left it for now.

Signed-off-by: Paul Holzinger <pholzing@redhat.com>

test/system/255-auto-update.bats

@@ -132,7 +132,6 @@ function _confirm_update() {
     # Image has already been pulled, so this shouldn't take too long
     local timeout=10
     while [[ $timeout -gt 0 ]]; do
-        sleep 1
         run_podman '?' inspect --format "{{.Image}}" $cname
         if [[ $status != 0 ]]; then
             if [[ $output =~ (no such object|does not exist in database): ]]; then
@@ -144,6 +143,7 @@ function _confirm_update() {
         elif [[ $output != $old_iid ]]; then
             return
         fi
+        sleep 1
         timeout=$((timeout - 1))
     done
 
@@ -417,7 +417,7 @@ EOF
 Description=Podman auto-update testing timer
 
 [Timer]
-OnCalendar=*-*-* *:*:0/2
+OnActiveSec=0s
 Persistent=true
 
 [Install]