Fix leap to SLES15.2 gnome migration waiting for display manager issue

In leap to SLES15.2 gnome zypper migration test, we need to skip the wait for display
manager step.

Because in the creating of qcow file phrase, we choose the auto login option in the
installation. so after the installation the system will boot directly into the generic
desktop. So in our migration test the leap will boot directly into the generic desktop.
We don't need to wait the display manager as the SLES do.

tests/boot/snapper_rollback.pm

@@ -18,12 +18,17 @@ use warnings;
 use migration 'check_rollback_system';
 use power_action_utils 'power_action';
 use Utils::Backends 'is_pvm';
+use version_utils;
 
 sub run {
     my ($self) = @_;
-
-    if (!check_screen 'linux-login', 200) {
-        assert_screen 'displaymanager', 90;
+    if (is_leap_migration && check_var('DESKTOP', 'gnome')) {
+        assert_screen 'generic-desktop', 90;
+    }
+    else {
+        if (!check_screen 'linux-login', 200) {
+            assert_screen 'displaymanager', 90;
+        }
     }
     select_console 'root-console';
     # 1)

tests/migration/online_migration/zypper_migration.pm

@@ -138,7 +138,7 @@ sub run {
     # with other than the SAP Administrator
     #
     # sometimes reboot takes longer time after online migration, give more time
-    $self->wait_boot(textmode => !is_desktop_installed, bootloader_time => 300, ready_time => 600, nologin => (is_sles4sap || is_leap_migration));
+    $self->wait_boot(textmode => !is_desktop_installed, bootloader_time => 300, ready_time => 600, nologin => is_sles4sap);
 }
 
 1;