Fixes to support Java11 HTTP/2 client

Author: shorea

core/auth/src/main/java/software/amazon/awssdk/auth/signer/internal/AbstractAws4Signer.java

@@ -56,7 +56,8 @@ public abstract class AbstractAws4Signer<T extends Aws4SignerParams, U extends A
     private static final int SIGNER_CACHE_MAX_SIZE = 300;
     private static final FifoCache<SignerKey> SIGNER_CACHE =
         new FifoCache<>(SIGNER_CACHE_MAX_SIZE);
-    private static final List<String> LIST_OF_HEADERS_TO_IGNORE_IN_LOWER_CASE = Arrays.asList("connection", "x-amzn-trace-id");
+    private static final List<String> LIST_OF_HEADERS_TO_IGNORE_IN_LOWER_CASE =
+        Arrays.asList("connection", "x-amzn-trace-id", "user-agent");
 
     protected SdkHttpFullRequest.Builder doSign(SdkHttpFullRequest request,
                                                 Aws4SignerRequestParams requestParams,

core/sdk-core/src/main/java/software/amazon/awssdk/core/internal/http/async/SimpleRequestProvider.java

@@ -78,9 +78,9 @@ public void request(long n) {
             if (n <= 0) {
                 s.onError(new IllegalArgumentException("Demand must be positive"));
             } else if (running) {
+                running = false;
                 s.onNext(ByteBuffer.wrap(content));
                 s.onComplete();
-                running = false;
             }
         }