Allow creation of integration tests

- created an interface IntegrationTest that marks integration tests
- modified JUnit plugin rules in pom file to not run integration tests
  by default
- marked FlowPusherTest as an integration test

Change-Id: I9719465afd365802377e110e44824fe111cb44c4
diff --git a/pom.xml b/pom.xml
index 4a7fc59..2209d2f 100644
--- a/pom.xml
+++ b/pom.xml
@@ -111,6 +111,7 @@
         <configuration>
           <argLine>-XX:MaxPermSize=256m</argLine>
           <redirectTestOutputToFile>true</redirectTestOutputToFile>
+          <excludedGroups>net.onrc.onos.core.util.IntegrationTest</excludedGroups>
         </configuration>
       </plugin>
       <!-- exec:java -->