nixos tests: waitForWindow: output a list of windows we see prior to the final check

    machine: must succeed: xwininfo -root -tree | sed 's/.*0x[0-9a-f]* \"\([^\"]*\)\".*/\1/; t; d'
    machine: exit status 0
    machine: Last chance to match /(?^:dfiirst configuration)/ on the the window list, which currently contains:
    machine: [i3 con] container around 0xf8a5f0, i3: first configuration, [i3 con] floatingcon around 0xf8c260, [i3 con] container around 0xf8a380, i3bar for output Virtual-1, [i3 con] bottom dockarea Virtual-1, [i3 con] workspace 1, [i3 con] content Virtual-1, [i3 con] top dockarea Virtual-1, [i3 con] output Virtual-1, [i3 con] workspace __i3_scratch, [i3 con] content __i3, [i3 con] pseudo-output __i3, i3