test/with-term: log output before close

[abhinav]

We're seeing flakiness on tests relying on with-term.
Output doesn't include what went wrong because it's all going
to the terminal emulator.

Log the output on failure.

[abhinav]

This change is part of the following stack:

• test/with-term: log output before close #1060 ◀

_{Change managed by git-spice.}