DRILL-6591: Show Exception for failed queries submitted in WebUI

* DRILL-6591: Show Exception for failed queries submitted in WebUI

When query fails on Web UI result page no error is shown, only "No result found." 
This was because DRILL-6477 (PR #1309) switched to `WebUserConnection.await(long timeoutInMillis)` . Unlike the original `WebUserConnection.await()`, this method did not throw any UserException generated by a query failure. The fix was to use WebUserConnection.getError() method to know about failure of the query and throw UserRemoteException with that.

closes #1379

exec/java-exec/src/main/java/org/apache/drill/exec/server/rest/QueryWrapper.java

@@ -22,6 +22,7 @@
 import com.google.common.collect.Maps;
 
 import org.apache.drill.common.exceptions.UserException;
+import org.apache.drill.common.exceptions.UserRemoteException;
 import org.apache.drill.exec.proto.UserBitShared.QueryId;
 import org.apache.drill.exec.proto.UserBitShared.QueryResult.QueryState;
 import org.apache.drill.exec.proto.UserBitShared.QueryType;
@@ -86,9 +87,8 @@ public QueryResult run(final WorkManager workManager, final WebUserConnection we
     logger.debug("Wait until the query execution is complete or there is error submitting the query");
     do {
       try {
-        isComplete = webUserConnection.await(TimeUnit.SECONDS.toMillis(1)); /*periodically timeout to check heap*/
-      } catch (Exception e) { }
-
+        isComplete = webUserConnection.await(TimeUnit.SECONDS.toMillis(1)); //periodically timeout 1 sec to check heap
+      } catch (InterruptedException e) {}
       usagePercent = getHeapUsage();
       if (usagePercent >  HEAP_MEMORY_FAILURE_THRESHOLD) {
         nearlyOutOfHeapSpace = true;
@@ -97,21 +97,22 @@ public QueryResult run(final WorkManager workManager, final WebUserConnection we
 
     //Fail if nearly out of heap space
     if (nearlyOutOfHeapSpace) {
+      UserException almostOutOfHeapException = UserException.resourceError()
+          .message("There is not enough heap memory to run this query using the web interface. ")
+          .addContext("Please try a query with fewer columns or with a filter or limit condition to limit the data returned. ")
+          .addContext("You can also try an ODBC/JDBC client. ")
+          .build(logger);
+      //Add event
       workManager.getBee().getForemanForQueryId(queryId)
-        .addToEventQueue(QueryState.FAILED,
-            UserException.resourceError(
-                new Throwable(
-                    "There is not enough heap memory to run this query using the web interface. "
-                    + "Please try a query with fewer columns or with a filter or limit condition to limit the data returned. "
-                    + "You can also try an ODBC/JDBC client. "
-                    )
-                )
-              .build(logger)
-            );
+        .addToEventQueue(QueryState.FAILED, almostOutOfHeapException);
+      //Return NearlyOutOfHeap exception
+      throw almostOutOfHeapException;
     }
 
-    if (logger.isTraceEnabled()) {
-      logger.trace("Query {} is completed ", queryId);
+    logger.trace("Query {} is completed ", queryId);
+
+    if (webUserConnection.getError() != null) {
+      throw new UserRemoteException(webUserConnection.getError());
     }
 
     if (webUserConnection.results.isEmpty()) {