Update Checkstyle config to ignore generated sources

Change-Id: Iaead8d846cb1bd2e9240bc52ee0feabdfd3ffddf

tools/checkstyle.xml

diff --git a/tools/checkstyle.xml b/tools/checkstyle.xml
index fc94144..1bb40f7 100644
--- a/tools/checkstyle.xml
+++ b/tools/checkstyle.xml
@@ -104,4 +104,7 @@
     <property name="checkFormat" value="$1"/>
     <property name="influenceFormat" value="$2"/>
   </module>
+  <module name="SuppressionFilter">
+    <property name="file" value="${samedir}/checkstyle_suppressions.xml"/>
+  </module>
 </module>