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

1 files changed, 15 insertions, 4 deletions

diff --git a/src/migration-scripts/system/31-to-32 b/src/migration-scripts/system/31-to-32
index b68dab34f..e92473835 100644
--- a/src/migration-scripts/system/31-to-32
+++ b/src/migration-scripts/system/31-to-32
@@ -16,23 +16,34 @@
 # Serial
 
 from vyos.configtree import ConfigTree
+from vyos.flavor import get_image_serial_console
 from vyos.system import disk
 from vyos.system.grub import CFG_VYOS_VARS
 from vyos.system.grub import vars_read
 
-serial_console = 'ttyS0'
 base = ['system', 'console']
 
 def migrate(config: ConfigTree) -> None:
     if not config.exists(base):
         return
 
+    # The serial console device is defined by the image flavor - amd64 uses the
+    # 8250 UART at ttyS0 while arm64 systems expose the PL011 UART as ttyAMA0
+    console_type, console_num, _ = get_image_serial_console()
+    if not console_type:
+        # image flavor carries no serial console data, assume 8250 UART
+        console_type, console_num = 'ttyS', '0'
+    serial_console = f'{console_type}{console_num}'
+
     root_dir = disk.find_persistence()
     vars_file: str = f'{root_dir}/{CFG_VYOS_VARS}'
     vars_current: dict[str, str] = vars_read(vars_file)
+    # A system without persistent GRUB storage - like VyOS running inside a
+    # container - has no boot console we could detect
+    if not vars_current:
+        return
+
     # Check if VyOS installation uses serial boot console
-    if vars_current['console_type'] == 'ttyS':
-        # In the past we only supported ttyS0 as boot console, that's why we
-        # can hardcode it ...
+    if vars_current['console_type'] == console_type:
         if config.exists(base + ['device', serial_console]):
             config.set(base + ['device', serial_console, 'kernel'])