kunit: tool: cosmetic: don't specify duplicate kernel cmdline options

Context:
When using a non-UML arch, kunit.py will boot the test kernel with
options like these by default (this is x86_64):
> mem=1G console=tty kunit_shutdown=halt console=ttyS0 kunit_shutdown=reboot

The first three options are added unconditionally but are only intended
for UML.

1. 'mem=1G' is redundant with the '-m 1024' that we hard-code into the
   qemu commandline.

2. We specify a 'console' for all tools/testing/kunit/qemu_configs/*.py
   already, so 'console=tty' gets overwritten.

3. For QEMU, we need to use 'reboot', and for UML we need to use 'halt'.
   If you switch them, kunit.py will hang until the --timeout expires.

This patch:
Having these duplicate options is a bit noisy.
Switch so we only add UML-specific options for UML.

I.e. we now get
UML: 'mem=1G console=tty kunit_shutdown=halt' (unchanged)
x86_64: 'console=ttyS0 kunit_shutdown=reboot'

Side effect: you can't overwrite these options on UML w/ --kernel_arg.
But you already couldn't for QEMU (console, kunit_shutdown), and why
would you want to?
Signed-off-by: Daniel Latypov <dlatypov@google.com>
Reviewed-by: David Gow <davidgow@google.com>
Reviewed-by: Brendan Higgins <brendanhiggins@google.com>
Signed-off-by: Shuah Khan <skhan@linuxfoundation.org>

tools/testing/kunit/kunit_kernel.py

@@ -160,6 +160,7 @@ class LinuxSourceTreeOperationsUml(LinuxSourceTreeOperations):
 	def start(self, params: List[str], build_dir: str) -> subprocess.Popen:
 		"""Runs the Linux UML binary. Must be named 'linux'."""
 		linux_bin = os.path.join(build_dir, 'linux')
+		params.extend(['mem=1G', 'console=tty', 'kunit_shutdown=halt'])
 		return subprocess.Popen([linux_bin] + params,
 					   stdin=subprocess.PIPE,
 					   stdout=subprocess.PIPE,
@@ -330,7 +331,6 @@ class LinuxSourceTree:
 	def run_kernel(self, args=None, build_dir='', filter_glob='', timeout=None) -> Iterator[str]:
 		if not args:
 			args = []
-		args.extend(['mem=1G', 'console=tty', 'kunit_shutdown=halt'])
 		if filter_glob:
 			args.append('kunit.filter_glob='+filter_glob)