[SPARK-13823][CORE][STREAMING][SQL] Always specify Charset in String <-> byte[] conversions (and remaining Coverity items)

## What changes were proposed in this pull request?

- Fixes calls to `new String(byte[])` or `String.getBytes()` that rely on platform default encoding, to use UTF-8
- Same for `InputStreamReader` and `OutputStreamWriter` constructors
- Standardizes on UTF-8 everywhere
- Standardizes specifying the encoding with `StandardCharsets.UTF-8`, not the Guava constant or "UTF-8" (which means handling `UnuspportedEncodingException`)
- (also addresses the other remaining Coverity scan issues, which are pretty trivial; these are separated into commit https://github.com/srowen/spark/commit/1deecd8d9ca986d8adb1a42d315890ce5349d29c )

## How was this patch tested?

Jenkins tests

Author: Sean Owen <sowen@cloudera.com>

Closes #11657 from srowen/SPARK-13823.

1 files changed, 4 insertions, 2 deletions

diff --git a/docs/streaming-custom-receivers.md b/docs/streaming-custom-receivers.md
index 8454774861..732c83dc84 100644
--- a/docs/streaming-custom-receivers.md
+++ b/docs/streaming-custom-receivers.md
@@ -72,7 +72,8 @@ class CustomReceiver(host: String, port: Int)
      socket = new Socket(host, port)
 
      // Until stopped or connection broken continue reading
-     val reader = new BufferedReader(new InputStreamReader(socket.getInputStream(), "UTF-8"))
+     val reader = new BufferedReader(
+       new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8))
      userInput = reader.readLine()
      while(!isStopped && userInput != null) {
        store(userInput)
@@ -135,7 +136,8 @@ public class JavaCustomReceiver extends Receiver<String> {
       // connect to the server
       socket = new Socket(host, port);
 
-      BufferedReader reader = new BufferedReader(new InputStreamReader(socket.getInputStream()));
+      BufferedReader reader = new BufferedReader(
+        new InputStreamReader(socket.getInputStream(), StandardCharsets.UTF_8));
 
       // Until stopped or connection broken continue reading
       while (!isStopped() && (userInput = reader.readLine()) != null) {