kunit: tool: Allow overriding the shutdown mode from qemu config

Not all platforms support machine reboot.
If it a proper reboot is not supported the machine will hang.
Allow the QEMU configuration to override the necessary shutdown mode for
the specific system under test.

Link: https://lore.kernel.org/r/20241111-kunit-loongarch-v2-2-7676eb5f2da3@linutronix.de
Signed-off-by: Thomas Weißschuh <thomas.weissschuh@linutronix.de>
Reviewed-by: David Gow <davidgow@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

Author: t-8ch

tools/testing/kunit/kunit_kernel.py

@@ -105,7 +105,9 @@ def __init__(self, qemu_arch_params: qemu_config.QemuArchParams, cross_compile:
 		self._kconfig = qemu_arch_params.kconfig
 		self._qemu_arch = qemu_arch_params.qemu_arch
 		self._kernel_path = qemu_arch_params.kernel_path
-		self._kernel_command_line = qemu_arch_params.kernel_command_line + ' kunit_shutdown=reboot'
+		self._kernel_command_line = qemu_arch_params.kernel_command_line
+		if 'kunit_shutdown=' not in self._kernel_command_line:
+			self._kernel_command_line += ' kunit_shutdown=reboot'
 		self._extra_qemu_params = qemu_arch_params.extra_qemu_params
 		self._serial = qemu_arch_params.serial