test: several cleanups for DeferReactivation=

test: several cleanups for DeferReactivation=

- move to TEST-07-PID1, as it is a timer setting,
- rename the timer and service, to emphasize they are for testing
  DeferReactivation=,
- use timeout command to wait for the timer being triggered several times,
- stop the timer when not necessary,
- accept 9 seconds as delta, as there are fluctuations.

Fixes the following failure:
```
TEST-74-AUX-UTILS.sh[422]: + last=
TEST-74-AUX-UTILS.sh[422]: + read -r time
TEST-74-AUX-UTILS.sh[422]: + '[' -n '' ']'
TEST-74-AUX-UTILS.sh[422]: + last=1753779616
TEST-74-AUX-UTILS.sh[422]: + read -r time
TEST-74-AUX-UTILS.sh[422]: + '[' -n 1753779616 ']'
TEST-74-AUX-UTILS.sh[422]: + delta=9
TEST-74-AUX-UTILS.sh[422]: + '[' 9 -lt 10 ']'
TEST-74-AUX-UTILS.sh[422]: + echo 'Timer fired too early: 9 < 10'
```

Fixes #38403.