agent: Implement pty option for CockpitTextStream

This lets us open a pty by specifying 'pty': true in the channel
options.
web: Implement a proper terminal on rescue terminal page

Use a proper terminal from term.js on the terminal page.

Fixes #434
Cloles #472
common: Tweak test output a bit

For more visibility in CI. Also remove unnecessary init
from test-pipe.c