tests: refactor EthernetFixture

Also, use BOOST_TEST_INFO_SCOPE in a few places.

Change-Id: I113f326207825949ed9d3d22ade0654976d49b76
diff --git a/tests/daemon/mgmt/fib-manager.t.cpp b/tests/daemon/mgmt/fib-manager.t.cpp
index 32bbec3..5da697b 100644
--- a/tests/daemon/mgmt/fib-manager.t.cpp
+++ b/tests/daemon/mgmt/fib-manager.t.cpp
@@ -421,6 +421,7 @@
   std::vector<ndn::nfd::FibEntry> receivedRecords, expectedRecords;
   for (size_t idx = 0; idx < nEntries; ++idx) {
     ndn::nfd::FibEntry decodedEntry(content.elements()[idx]);
+    BOOST_TEST_INFO_SCOPE(decodedEntry);
     receivedRecords.push_back(decodedEntry);
     actualPrefixes.erase(decodedEntry.getPrefix());