[SPARK-13823][SPARK-13397][SPARK-13395][CORE] More warnings, StandardCharset follow up

## What changes were proposed in this pull request?

Follow up to https://github.com/apache/spark/pull/11657

- Also update `String.getBytes("UTF-8")` to use `StandardCharsets.UTF_8`
- And fix one last new Coverity warning that turned up (use of unguarded `wait()` replaced by simpler/more robust `java.util.concurrent` classes in tests)
- And while we're here cleaning up Coverity warnings, just fix about 15 more build warnings

## How was this patch tested?

Jenkins tests

Author: Sean Owen <sowen@cloudera.com>

Closes #11725 from srowen/SPARK-13823.2.

1 files changed, 2 insertions, 6 deletions

diff --git a/common/sketch/src/main/java/org/apache/spark/util/sketch/Utils.java b/common/sketch/src/main/java/org/apache/spark/util/sketch/Utils.java
index feb601d44f..81461f0300 100644
--- a/common/sketch/src/main/java/org/apache/spark/util/sketch/Utils.java
+++ b/common/sketch/src/main/java/org/apache/spark/util/sketch/Utils.java
@@ -17,15 +17,11 @@
 
 package org.apache.spark.util.sketch;
 
-import java.io.UnsupportedEncodingException;
+import java.nio.charset.StandardCharsets;
 
 class Utils {
   public static byte[] getBytesFromUTF8String(String str) {
-    try {
-      return str.getBytes("utf-8");
-    } catch (UnsupportedEncodingException e) {
-      throw new IllegalArgumentException("Only support utf-8 string", e);
-    }
+    return str.getBytes(StandardCharsets.UTF_8);
   }
 
   public static long integralToLong(Object i) {