[trac606] use a local dir for xfrout log to suppress warning in tests.

tests/system/glue/nsx1/b10-config.db.in

@@ -2,5 +2,8 @@
  "Auth": {
    "listen_on": [{"address": "10.53.0.1", "port": 5300}],
    "database_file": "@abs_builddir@/zone.sqlite3"
+ },
+ "Xfrout": {
+   "log_file": "@abs_builddir@/Xfrout.log"
  }
 }