tests: add FreshnessPeriod where MustBeFresh is used

Also, set MustBeFresh in autoconfig-server HubData test,
to reflect the behavior of autoconfig client.

refs #4913

Change-Id: I0af29378630a2208e98ef0913d83668a603e9a88
diff --git a/tests/tools/mock-nfd-mgmt-fixture.hpp b/tests/tools/mock-nfd-mgmt-fixture.hpp
index 1e1d592..7b43ea9 100644
--- a/tests/tools/mock-nfd-mgmt-fixture.hpp
+++ b/tests/tools/mock-nfd-mgmt-fixture.hpp
@@ -191,6 +191,7 @@
     }
 
     auto data = make_shared<Data>(name);
+    data->setFreshnessPeriod(1_s);
     data->setFinalBlock(name[-1]);
     data->setContent(std::forward<ContentArgs>(contentArgs)...);
     this->signDatasetReply(*data);