tests/functional: Move the check for the parameters from avocado to functional

tests/functional: Move the check for the parameters from avocado to functional

test_x86_64_pc in tests/avocado/boot_linux_console.py only checks
whether the kernel parameters have correctly been passed to the
kernel in the guest by looking for them in the console output of the
guest. Let's move that to the functional test framework now, but
instead of doing it in a separate test, let's do it for all tuxrun
tests instead, so it is done automatically for all targets that have
a tuxrun test.

Reviewed-by: Daniel P. Berrangé <berrange@redhat.com>
Message-ID: <20250414113031.151105-3-thuth@redhat.com>
Signed-off-by: Thomas Huth <thuth@redhat.com>