[SPARK-23197][DSTREAMS] Increased timeouts to resolve flakiness

## What changes were proposed in this pull request?

Increased timeout from 50 ms to 300 ms (50 ms was really too low).

## How was this patch tested?
Multiple rounds of tests.

Author: Tathagata Das <tathagata.das1565@gmail.com>

Closes #20371 from tdas/SPARK-23197.

streaming/src/test/scala/org/apache/spark/streaming/ReceiverSuite.scala

@@ -105,13 +105,13 @@ class ReceiverSuite extends TestSuiteBase with TimeLimits with Serializable {
     assert(executor.errors.head.eq(exception))
 
     // Verify restarting actually stops and starts the receiver
-    receiver.restart("restarting", null, 100)
-    eventually(timeout(50 millis), interval(10 millis)) {
+    receiver.restart("restarting", null, 600)
+    eventually(timeout(300 millis), interval(10 millis)) {
       // receiver will be stopped async
       assert(receiver.isStopped)
       assert(receiver.onStopCalled)
     }
-    eventually(timeout(1000 millis), interval(100 millis)) {
+    eventually(timeout(1000 millis), interval(10 millis)) {
       // receiver will be started async
       assert(receiver.onStartCalled)
       assert(executor.isReceiverStarted)