Turn cobertura quiet mode

- INFO message to stderr by Cobertura command was incorrectly
  interpreted by Jenkins' Maven log parser as an ERROR.
  Enabled quiet option to suppress INFO message to stderr.

Change-Id: I8ad36283b31e29e87aa207bc5e6fc7aaecd9293c
diff --git a/pom.xml b/pom.xml
index 1de66ca..c4568fb 100644
--- a/pom.xml
+++ b/pom.xml
@@ -258,6 +258,7 @@
               <exclude>net/floodlightcontroller/**/web/**/*.class</exclude>
             </excludes>
           </instrumentation>
+          <quiet>true</quiet>
         </configuration>
         <executions>
           <execution>
@@ -710,6 +711,7 @@
               <formats>
                 <format>xml</format>
               </formats>
+              <quiet>true</quiet>
             </configuration>
             <executions>
               <execution>