dhcp client: add unittest for DeviceInfo

Add unittest for DeviceInfo class.

Fix a comment in main.cc.

Bug: 25642025
TEST=compile and run unittest

Change-Id: Iffd90dc6581aaa3b6f44d5e6c92146275f88ccaf
diff --git a/dhcp_client.gyp b/dhcp_client.gyp
index 2638419..c2a7c0f 100644
--- a/dhcp_client.gyp
+++ b/dhcp_client.gyp
@@ -71,5 +71,21 @@
       ],
     },
   ],
+  'conditions': [
+    ['USE_test == 1', {
+      'targets': [
+        {
+          'target_name': 'dhcp_client_testrunner',
+          'type': 'executable',
+          'dependencies': ['libdhcp_client'],
+          'includes': ['../../../../platform2/common-mk/common_test.gypi'],
+          'sources': [
+            'device_info_unittest.cc',
+            'testrunner.cc',
+          ],
+        },
+      ],
+    }],
+  ],
 }