[java] Fix TestKuduPartitioner errorprone warning

This fixes the following errorprone warning:

Expression of type int may overflow before being assigned to a long
long upperBound = timeoutMs * 2; // Add 100% to avoid flakiness.

Change-Id: I9fd41b7cae9502468728efbdf51e3d7191447371
Reviewed-on: http://gerrit.cloudera.org:8080/14488
Tested-by: Kudu Jenkins
Reviewed-by: Adar Dembo <adar@cloudera.com>
diff --git a/java/kudu-client/src/test/java/org/apache/kudu/client/TestKuduPartitioner.java b/java/kudu-client/src/test/java/org/apache/kudu/client/TestKuduPartitioner.java
index 400c8e6..1153051 100644
--- a/java/kudu-client/src/test/java/org/apache/kudu/client/TestKuduPartitioner.java
+++ b/java/kudu-client/src/test/java/org/apache/kudu/client/TestKuduPartitioner.java
@@ -184,7 +184,7 @@
       assertTrue(ex.getMessage().startsWith("cannot complete before timeout"));
     }
     long elapsed = System.currentTimeMillis() - now;
-    long upperBound = timeoutMs * 2; // Add 100% to avoid flakiness.
+    long upperBound = timeoutMs * 2L; // Add 100% to avoid flakiness.
     assertTrue(String.format("Elapsed time %d exceeded upper bound %d", elapsed, upperBound),
                elapsed <= upperBound);
   }