nixos/testing: Fix tty output

Prior to this contribution, the Kernel's frame buffer output
boot log wasn't visible on the graphical console.

Now, we can also test applications with graphical output that run
during the boot process.

nixos/modules/testing/test-instrumentation.nix

@@ -162,6 +162,7 @@ in
 
     boot.kernelParams = [
       "console=${qemu-common.qemuSerialDevice}"
+      "console=tty0"
       # Panic if an error occurs in stage 1 (rather than waiting for
       # user intervention).
       "panic=1" "boot.panic_on_fail"
@@ -180,6 +181,7 @@ in
     services.journald.extraConfig =
       ''
         ForwardToConsole=yes
+        TTYPath=/dev/${qemu-common.qemuSerialDevice}
         MaxLevelConsole=debug
       '';