core: limit the length of the confirmation question

core: limit the length of the confirmation question

When "confirmation_spawn=1", the confirmation question can look like:

  Execute /usr/bin/kmod static-nodes --format=tmpfiles --output=/run/tmpfiles.d/kmod.conf? [Yes, No, Skip]

which is pretty verbose and might not fit in the console width size (which is
usually 80 chars) and thus question will be splitted into 2 consecutive lines.

However since the question is now refreshed every 2 secs, the reprinted
question will overwrite the second line of the previous one...

To prevent this, this patch makes sure that the command line won't be longer
than 60 chars by ellipsizing it if the command is longer:

  Execute /usr/bin/kmod static-nodes --format=tmpfiles --output=/ru…nf? [Yes, No, View, Skip]

A following patch will introduce a new choice that will allow the user to get
details on the command to be executed so it will still be possible to see the
full command line.