qemu: Correctly wait for spice to migrate

Currently we query-spice after the main migration has completed
before moving to next state. Qemu reports this as boolean (not
enclosed within quotes). Therefore it is not correct to use
virJSONValueObjectGetString but virJSONValueObjectGetBoolean instead.

src/qemu/qemu_monitor_json.c

@@ -2399,7 +2399,6 @@ qemuMonitorJSONSpiceGetMigrationStatusReply(virJSONValuePtr reply,
                                             bool *spice_migrated)
 {
     virJSONValuePtr ret;
-    const char *migrated_str;
 
     if (!(ret = virJSONValueObjectGet(reply, "return"))) {
         virReportError(VIR_ERR_INTERNAL_ERROR, "%s",
@@ -2407,13 +2406,11 @@ qemuMonitorJSONSpiceGetMigrationStatusReply(virJSONValuePtr reply,
         return -1;
     }
 
-    if (!(migrated_str = virJSONValueObjectGetString(ret, "migrated"))) {
+    if (virJSONValueObjectGetBoolean(ret, "migrated", spice_migrated) < 0) {
         /* Deliberately don't report error here as we are
          * probably dealing with older qemu which doesn't
          * report this yet. Pretend spice is migrated. */
         *spice_migrated = true;
-    } else {
-        *spice_migrated = STREQ(migrated_str, "true");
     }
 
     return 0;