The notification is supposed to read "Reboot when it is convenient - to
install the updates", but I kept reading it as "Reboot - when it is
convenient to install the updates.", and I couldn't figure out the
"correct" punctuation to do that while remaining proper English. So move
the wording about instead.

Pipe success is determined by the success of the last command in the
pipe, and `grep` indicates failure if no lines were selected. If we
don't download anything then `grep` fails, the pipe fails, and the
script - due to `set -e` - then fails/aborts at that point.

So pipe through `cat` last, which always succeeds.

Don't care about the "Reading package lists..." and other interactive
fripperies, or the list of packages no longer required, or the full list
of packages to be upgraded, every time we just want to download new
updates. But logging the actual downloads is kinda useful, so keep
those.

To allow for kernel upgrades, which install new packages.

Also, make the way we pass options to `apt-get upgrade` more consistent
between calls. Notably, put all options before the command, as indicated
by the apt-get(1) man page.