Improve handling of logging in override targets

Improve handling of logging in override targets

Changes in 76ef1cbd64829ee4a5156a5fc4b887bcba6b974f broke
--remaining-packages in override target.

Now all debhelper commands run in the override target are marked as running
as part of the override, and when the whole target is run, the log is
updated to indicate that commands run during the override have finished.

So, inside the override target, --remaining-packages will see the commands
run as part of the target as having been run. Outside, if the target
fails, dh won't see the commands run it it as having been run.

Closes: #612828