[SPARK-14884][SQL][STREAMING][WEBUI] Fix call site for continuous queries

## What changes were proposed in this pull request?

Since we've been processing continuous queries in separate threads, the call sites are then `run at <unknown>:0`. It's not wrong but provides very little information; in addition, we can not distinguish two queries only from their call sites.

This patch fixes this.

### Before
[Jobs Tab]
![s1a](https://cloud.githubusercontent.com/assets/15843379/14766101/a47246b2-0a30-11e6-8d81-06a9a600113b.png)
[SQL Tab]
![s1b](https://cloud.githubusercontent.com/assets/15843379/14766102/a4750226-0a30-11e6-9ada-773d977d902b.png)
### After
[Jobs Tab]
![s2a](https://cloud.githubusercontent.com/assets/15843379/14766104/a89705b6-0a30-11e6-9830-0d40ec68527b.png)
[SQL Tab]
![s2b](https://cloud.githubusercontent.com/assets/15843379/14766103/a8966728-0a30-11e6-8e4d-c2e326400478.png)

## How was this patch tested?

Manually checks - see screenshots above.

Author: Liwei Lin <lwlin7@gmail.com>

Closes #12650 from lw-lin/fix-call-site.

sql/core/src/main/scala/org/apache/spark/sql/execution/SQLExecution.scala

@@ -23,7 +23,6 @@ import org.apache.spark.SparkContext
 import org.apache.spark.sql.SparkSession
 import org.apache.spark.sql.execution.ui.{SparkListenerSQLExecutionEnd,
   SparkListenerSQLExecutionStart}
-import org.apache.spark.util.Utils
 
 private[sql] object SQLExecution {
 
@@ -46,7 +45,11 @@ private[sql] object SQLExecution {
       val executionId = SQLExecution.nextExecutionId
       sc.setLocalProperty(EXECUTION_ID_KEY, executionId.toString)
       val r = try {
-        val callSite = Utils.getCallSite()
+        // sparkContext.getCallSite() would first try to pick up any call site that was previously
+        // set, then fall back to Utils.getCallSite(); call Utils.getCallSite() directly on
+        // continuous queries would give us call site like "run at <unknown>:0"
+        val callSite = sparkSession.sparkContext.getCallSite()
+
         sparkSession.sparkContext.listenerBus.post(SparkListenerSQLExecutionStart(
           executionId, callSite.shortForm, callSite.longForm, queryExecution.toString,
           SparkPlanInfo.fromSparkPlan(queryExecution.executedPlan), System.currentTimeMillis()))

sql/core/src/main/scala/org/apache/spark/sql/execution/streaming/StreamExecution.scala

@@ -36,7 +36,7 @@ import org.apache.spark.sql.catalyst.util._
 import org.apache.spark.sql.execution.QueryExecution
 import org.apache.spark.sql.util.ContinuousQueryListener
 import org.apache.spark.sql.util.ContinuousQueryListener._
-import org.apache.spark.util.UninterruptibleThread
+import org.apache.spark.util.{UninterruptibleThread, Utils}
 
 /**
  * Manages the execution of a streaming Spark SQL query that is occurring in a separate thread.
@@ -101,10 +101,18 @@ class StreamExecution(
   @volatile
   private[sql] var streamDeathCause: ContinuousQueryException = null
 
+  /* Get the call site in the caller thread; will pass this into the micro batch thread */
+  private val callSite = Utils.getCallSite()
+
   /** The thread that runs the micro-batches of this stream. */
   private[sql] val microBatchThread =
     new UninterruptibleThread(s"stream execution thread for $name") {
-      override def run(): Unit = { runBatches() }
+      override def run(): Unit = {
+        // To fix call site like "run at <unknown>:0", we bridge the call site from the caller
+        // thread to this micro batch thread
+        sparkSession.sparkContext.setCallSite(callSite)
+        runBatches()
+      }
     }
 
   /**