Added awaitInitialization call in all spark unit tests

Author: sapessi

aws-serverless-java-container-spark/src/test/java/com/amazonaws/serverless/proxy/spark/HelloWorldSparkTest.java

@@ -37,7 +37,7 @@ public static void initializeServer() {
             handler = SparkLambdaContainerHandler.getAwsProxyHandler();
 
             configureRoutes();
-
+            Spark.awaitInitialization();
         } catch (RuntimeException | ContainerInitializationException e) {
             e.printStackTrace();
             fail();

aws-serverless-java-container-spark/src/test/java/com/amazonaws/serverless/proxy/spark/InitExceptionHandlerTest.java

@@ -44,7 +44,7 @@ public void initException_mockException_expectHandlerToRun() {
                                                       serverFactory);
 
             configureRoutes();
-
+            Spark.awaitInitialization();
         } catch (Exception e) {
             e.printStackTrace();
             fail("Error while mocking server");

aws-serverless-java-container-spark/src/test/java/com/amazonaws/serverless/proxy/spark/SparkLambdaContainerHandlerTest.java

@@ -50,6 +50,8 @@ public void filters_onStartupMethod_executeFilters() {
 
         configureRoutes();
 
+        Spark.awaitInitialization();
+
         AwsProxyRequest req = new AwsProxyRequestBuilder().method("GET").path("/header-filter").build();
         AwsProxyResponse response = handler.proxy(req, new MockLambdaContext());
 
@@ -84,6 +86,7 @@ public void filters_unauthenticatedFilter_stopRequestProcessing() {
         });
 
         configureRoutes();
+        Spark.awaitInitialization();
 
         // first we test without the custom header, we expect request processing to complete
         // successfully