TEST-71-HOSTNAME: specify job mode for the stop job (#38413)

TEST-71-HOSTNAME: specify job mode for the stop job (#38413)

The CI run is failing in the stop command:
```
[ 4841.936906] TEST-71-HOSTNAME.sh[140]: + stop_hostnamed
[ 4841.936906] TEST-71-HOSTNAME.sh[140]: + systemctl stop systemd-hostnamed.service
[ 4845.959747] TEST-71-HOSTNAME.sh[226]: Job for systemd-hostnamed.service canceled.
[ 4846.013286] systemd[1]: TEST-71-HOSTNAME.service: Main process exited, code=exited, status=1/FAILURE
[ 4846.013792] systemd[1]: TEST-71-HOSTNAME.service: Failed with result 'exit-code'.
[ 4846.021821] systemd[1]: Failed to start TEST-71-HOSTNAME.service - TEST-71-HOSTNAME.
```
This happens when we create the stop job, but while we're waiting for
it to finish, something triggers a start of the unit and we lose to competing
start job.

Hopefully fixes #36089.