Handle and report exception thrown by checkstyle

Change-Id: I041fd0d4787ddff80a206e47688524984f3500ff
diff --git a/tools/build/conf/src/main/java/org/onosproject/buckdaemon/BuckDaemon.java b/tools/build/conf/src/main/java/org/onosproject/buckdaemon/BuckDaemon.java
index ce8a78c..5b37609 100644
--- a/tools/build/conf/src/main/java/org/onosproject/buckdaemon/BuckDaemon.java
+++ b/tools/build/conf/src/main/java/org/onosproject/buckdaemon/BuckDaemon.java
@@ -21,6 +21,7 @@
 import org.onosproject.checkstyle.CheckstyleRunner;
 
 import java.io.IOException;
+import java.io.PrintStream;
 import java.net.ServerSocket;
 import java.net.Socket;
 import java.nio.ByteBuffer;
@@ -176,9 +177,14 @@
                     BuckTask task = tasks.get(taskName);
                     if (task != null) {
                         System.out.println(String.format("Executing task '%s'", taskName));
-                        task.execute(context);
-                        for (String line : context.output()) {
-                            output(socket, line);
+                        try {
+                            task.execute(context);
+                            for (String line : context.output()) {
+                                output(socket, line);
+                            }
+                        // TODO should we catch Exception, RuntimeException, or something specific?
+                        } catch (Throwable e) {
+                            e.printStackTrace(new PrintStream(socket.getOutputStream()));
                         }
                     } else {
                         String message = String.format("No task named '%s'", taskName);
diff --git a/tools/build/conf/src/main/java/org/onosproject/checkstyle/CheckstyleRunner.java b/tools/build/conf/src/main/java/org/onosproject/checkstyle/CheckstyleRunner.java
index 25f3d53..65023b1 100644
--- a/tools/build/conf/src/main/java/org/onosproject/checkstyle/CheckstyleRunner.java
+++ b/tools/build/conf/src/main/java/org/onosproject/checkstyle/CheckstyleRunner.java
@@ -91,6 +91,7 @@
 
             listener.await();
         } catch (CheckstyleException | InterruptedException e) {
+            e.printStackTrace(); //dump exeception to stderr
             throw new RuntimeException(e);
         } finally {
             checker.destroy();