config_parser: Reduce number of file reads

This changes focuses on reducing the number of Parser() constructions to
limit the number of duplicate file reads.

Change-Id: I05df943844c70dc6aa729ab744d2d405cbfe2c76
Signed-off-by: William A. Kennington III <wak@google.com>
diff --git a/test/test_ethernet_interface.cpp b/test/test_ethernet_interface.cpp
index 96f00d1..e9ed3fd 100644
--- a/test/test_ethernet_interface.cpp
+++ b/test/test_ethernet_interface.cpp
@@ -43,8 +43,12 @@
     {
         mock_clear();
         mock_addIF("test0", 1, mac);
-        return {bus, "/xyz/openbmc_test/network/test0",
-                EthernetInterface::DHCPConf::none, manager, true};
+        return {bus,
+                "/xyz/openbmc_test/network/test0",
+                config::Parser(),
+                EthernetInterface::DHCPConf::none,
+                manager,
+                true};
     }
 
     int countIPObjects()