[SPARK-13117][WEB UI] WebUI should use the local ip not 0.0.0.0

## What changes were proposed in this pull request?

In WebUI, now Jetty Server starts with SPARK_LOCAL_IP config value if it
is configured otherwise it starts with default value as '0.0.0.0'.

It is continuation as per the closed PR https://github.com/apache/spark/pull/11133 for the JIRA SPARK-13117 and discussion in SPARK-13117.

## How was this patch tested?

This has been verified using the command 'netstat -tnlp | grep <PID>' to check on which IP/hostname is binding with the below steps.

In the below results, mentioned PID in the command is the corresponding process id.

#### Without the patch changes,
Web UI(Jetty Server) is not taking the value configured for SPARK_LOCAL_IP and it is listening to all the interfaces.
###### Master
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 3930
tcp6       0      0 :::8080                 :::*                    LISTEN      3930/java
```

###### Worker
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 4090
tcp6       0      0 :::8081                 :::*                    LISTEN      4090/java
```

###### History Server Process,
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 2471
tcp6       0      0 :::18080                :::*                    LISTEN      2471/java
```
###### Driver
```
[devarajstobdtserver2 spark-master]$ netstat -tnlp | grep 6556
tcp6       0      0 :::4040                 :::*                    LISTEN      6556/java
```

#### With the patch changes

##### i. With SPARK_LOCAL_IP configured
If the SPARK_LOCAL_IP is configured then all the processes Web UI(Jetty Server) is getting bind to the configured value.
###### Master
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 1561
tcp6       0      0 x.x.x.x:8080       :::*                    LISTEN      1561/java
```
###### Worker
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 2229
tcp6       0      0 x.x.x.x:8081       :::*                    LISTEN      2229/java
```
###### History Server
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 3747
tcp6       0      0 x.x.x.x:18080      :::*                    LISTEN      3747/java
```
###### Driver
```
[devarajstobdtserver2 spark-master]$ netstat -tnlp | grep 6013
tcp6       0      0 x.x.x.x:4040       :::*                    LISTEN      6013/java
```

##### ii. Without SPARK_LOCAL_IP configured
If the SPARK_LOCAL_IP is not configured then all the processes Web UI(Jetty Server) will start with the '0.0.0.0' as default value.
###### Master
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 4573
tcp6       0      0 :::8080                 :::*                    LISTEN      4573/java
```

###### Worker
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 4703
tcp6       0      0 :::8081                 :::*                    LISTEN      4703/java
```

###### History Server
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 4846
tcp6       0      0 :::18080                :::*                    LISTEN      4846/java
```

###### Driver
```
[devarajstobdtserver2 sbin]$ netstat -tnlp | grep 5437
tcp6       0      0 :::4040                 :::*                    LISTEN      5437/java
```

Author: Devaraj K <devaraj@apache.org>

Closes #11490 from devaraj-kavali/SPARK-13117-v1.

core/src/main/scala/org/apache/spark/ui/WebUI.scala

@@ -134,8 +134,10 @@ private[spark] abstract class WebUI(
   def bind() {
     assert(!serverInfo.isDefined, "Attempted to bind %s more than once!".format(className))
     try {
-      serverInfo = Some(startJettyServer("0.0.0.0", port, sslOptions, handlers, conf, name))
-      logInfo("Started %s at http://%s:%d".format(className, publicHostName, boundPort))
+      var host = Option(conf.getenv("SPARK_LOCAL_IP")).getOrElse("0.0.0.0")
+      serverInfo = Some(startJettyServer(host, port, sslOptions, handlers, conf, name))
+      logInfo("Bound %s to %s, and started at http://%s:%d".format(className, host,
+        publicHostName, boundPort))
     } catch {
       case e: Exception =>
         logError("Failed to bind %s".format(className), e)