Enforce checkstyle for unit test codes

- First time contributer is likely to start with unit-test code,
  so it is probably better to enforce the ONOS code style for
  unit test codes also.

Change-Id: Id665e55b0f0bee7232dfb18ce6a7f9ea8cc3b164
diff --git a/.checkstyle b/.checkstyle
index 40e6b6c..de2d242 100644
--- a/.checkstyle
+++ b/.checkstyle
@@ -6,6 +6,6 @@
   </local-check-config>
   <fileset name="all" enabled="true" check-config-name="ONOS" local="true">
     <file-match-pattern match-pattern="." include-pattern="true"/>
-    <file-match-pattern match-pattern="src/test/.*" include-pattern="false"/>
+    <file-match-pattern match-pattern="src/test/.*" include-pattern="true"/>
   </fileset>
 </fileset-config>