smoketest: T9014: make configtest serial console image flavor agnostic

The configuration tests hardcoded "system console device ttyS0 speed 115200",
which only holds for amd64, whereas arm64 images expose the UART as ttyAMA0, so
loading these configs produced a diff against the assert data and the tests
failed.

Replace the hardcoded values in all config test inputs and their assert
counterparts with the @SERIAL_DEVICE@ and @SERIAL_SPEED@ placeholders. The
vyos-1x-smoketest postinst queries the image flavor and implants the real
values once at install time, so the test runner needs no runtime patching.

Migration script 31-to-32 now derives the serial device from the flavor, too,
instead of assuming ttyS0.

This can be observed during vyos-1x package installation while building the
ISO image

Setting up vyos-1x-smoketest (999.0-14834-g16f1cf457-dirty) ...
...
I: Implanted serial console ttyS0,115200 into /usr/libexec/vyos/tests/configs

0 files changed, 0 insertions, 0 deletions