migration-test: Be consistent for ppc

It makes no sense that we don't have the same configuration on both sides.

Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Message-ID: <20230608224943.3877-2-quintela@redhat.com>
Signed-off-by: Juan Quintela <quintela@redhat.com>

tests/qtest/migration-test.c

@@ -748,7 +748,7 @@ static int test_migrate_start(QTestState **from, QTestState **to,
                                       "'nvramrc=hex .\" _\" begin %x %x "
                                       "do i c@ 1 + i c! 1000 +loop .\" B\" 0 "
                                       "until'", end_address, start_address);
-        arch_target = g_strdup("");
+        arch_target = g_strdup("-nodefaults");
     } else if (strcmp(arch, "aarch64") == 0) {
         init_bootfile(bootpath, aarch64_kernel, sizeof(aarch64_kernel));
         machine_opts = "virt,gic-version=max";