update preview diff and merge proposal creation jobs OOPS reports are not logging request variables

Compare OOPS-1398UPD12 with OOPS-1398UPD13, the former contains request variables while the latter does not.

Looking at the raw log (i.e. the OOPS file on the filesystem) indicates that the request variables are not being logged.

Chex, Aaron and I did some investigation about this issue and discarded a few hypothesis.
- It doesn't seem to be a problem with oops-tools, since the raw log doesn't contain the request variable section;
- It doesn't seem to be a configuration that turns off logging of req vars for those scripts, since lp-production-configs/trunk/production/launchpad-lazr.conf have no option that could disable req vars logging only;
- there are no cowboyed changes on bzrsyncd, which is currently running r8653 (see https://pastebin.canonical.com/24944/)