Ensure correct value from/to SERIALCONSOLE

1.For OSD workers, some machines use ttyS0 and some others use ttyS1 or even ttyS2
which is assigned to setting SERIALDEV. But SERIALDEV is not safe enough to be used
everywhere, because it becomes sshserial during test run, here is an example:
https://openqa.suse.de/tests/21287146/file/vars.json.
2.Merge request https://gitlab.suse.de/openqa/salt-pillars-openqa/-/merge_requests/1225
introduces setting SERIALCONSOLE which is already being widely used in automation code.
This can avoid incorrect SERIALCONSOLE leading to test run failure, for exmaple:
https://openqa.suse.de/tests/21287262#step/prepare_transactional_server/74.
3.Current subroutine save_serial_console resets SERIALCONSOLE, if it has no value, to
default value obtained from SERIALDEV which may become sshserial. So it is necessary to
check and assign more meaningful default value ttyS1 to SERIALCONSOLE.

Author: waynechen55

lib/Utils/Backends.pm

@@ -64,6 +64,7 @@ sub save_serial_console {
     my $serialconsole = get_var('SERIALCONSOLE', '');
     return if ($serialconsole ne '');
     $serialconsole = get_var('SERIALDEV', 'ttyS1');
+    $serialconsole = 'ttyS1' if ($serialconsole eq 'sshserial');
     set_var('SERIALCONSOLE', $serialconsole);
     bmwqemu::save_vars();
 }