util: upgrade default $TERM from vt102 to vt220 if we have no idea about the connecte...

util: upgrade default $TERM from vt102 to vt220 if we have no idea about the connected terminal

So far, if we had no knowledge about the correct $TERM we defaulted to
v102, as a safe, conservative choice. However, the terminfo data for
vt102 is not aware of pageup/pagedown, which makes "less" much harder
work with than necessary. Setting vt220 allows them to work correctly.

"vt220" should be a sufficiently safe choice too, given that xterm,
gnome-terminal and the linux console all strive to implement vt220 as
baseline, already to pass pageup/pagedown correctly to apps.

Effectively, with this change "journalctl -e" run inside a
"systemd-nspawn" terminal will now run a pager where pageup/pagedown
works, which is quite an improvement of usability for containers.