tests/functional/aspeed: unify boot completion detection on 'login:' prompt

tests/functional/aspeed: unify boot completion detection on 'login:' prompt

The boot completion check in AspeedTest waits for the systemd
"Hostname set to" message, which occasionally causes intermittent test
timeouts, e.g. on ast2500 SoC machines. The root cause seems to be
console output interleaving of both systemd and the getty login
process. This results in the expected pattern string being broken up.

Unify and simplify all boot completion checks by looking for the
generic 'login:' substring in AspeedTest.wait_for_boot_complete().
With the override gone, remove the redundant FacebookAspeedTest class
and update the Anacapa, Bletchley, and Catalina tests to inherit
directly from AspeedTest. Also drop the now-dead image_hostname
parameter from do_test_arm_aspeed_openbmc().

Reported-by: Peter Maydell <peter.maydell@linaro.org>
Resolves: https://gitlab.com/qemu-project/qemu/-/work_items/3117
Reviewed-by: Thomas Huth <thuth@redhat.com>
Link: https://lore.kernel.org/qemu-devel/20260617042718.2883655-1-clg@redhat.com
Signed-off-by: Cédric Le Goater <clg@redhat.com>