[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.

2 files changed, 26 insertions, 6 deletions

diff --git a/common/sketch/pom.xml b/common/sketch/pom.xml
index 442043cb51..8bc1f52798 100644
--- a/common/sketch/pom.xml
+++ b/common/sketch/pom.xml
@@ -45,5 +45,29 @@
   <build>
     <outputDirectory>target/scala-${scala.binary.version}/classes</outputDirectory>
     <testOutputDirectory>target/scala-${scala.binary.version}/test-classes</testOutputDirectory>
+    <pluginManagement>
+      <plugins>
+        <plugin>
+          <groupId>net.alchim31.maven</groupId>
+          <artifactId>scala-maven-plugin</artifactId>
+          <configuration>
+            <javacArgs combine.children="append">
+              <!-- This option is needed to suppress warnings from sun.misc.Unsafe usage -->
+              <javacArg>-XDignore.symbol.file</javacArg>
+            </javacArgs>
+          </configuration>
+        </plugin>
+        <plugin>
+          <groupId>org.apache.maven.plugins</groupId>
+          <artifactId>maven-compiler-plugin</artifactId>
+          <configuration>
+            <compilerArgs combine.children="append">
+              <!-- This option is needed to suppress warnings from sun.misc.Unsafe usage -->
+              <arg>-XDignore.symbol.file</arg>
+            </compilerArgs>
+          </configuration>
+        </plugin>
+      </plugins>
+    </pluginManagement>
   </build>
 </project>
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) {