Remove unnecessary credentials retrieval (#34)

Just overriding the signer to a no-op signer in client config still
causes the default credentials provider chain to be invoked and fail in
the absence of credentials obtainable by the default chain. Instead,
build the client with anonymous credentials, which skips both signing
and credentials retrieval.

aws-xray-recorder-sdk-core/src/main/java/com/amazonaws/xray/strategy/sampling/XRayClient.java

@@ -1,23 +1,26 @@
 package com.amazonaws.xray.strategy.sampling;
 
 import com.amazonaws.ClientConfiguration;
-import com.amazonaws.auth.SignerFactory;
+import com.amazonaws.auth.AWSCredentialsProvider;
+import com.amazonaws.auth.AWSStaticCredentialsProvider;
+import com.amazonaws.auth.AnonymousAWSCredentials;
 import com.amazonaws.client.builder.AwsClientBuilder;
 import com.amazonaws.services.xray.AWSXRayClientBuilder;
 import com.amazonaws.services.xray.AWSXRay;
 import com.amazonaws.xray.config.DaemonConfiguration;
 
 public final class XRayClient {
 
-    private static final String DUMMY_REGION = "us-west-1"; // Ignored because we use a No-op signer
+    private static final AWSCredentialsProvider ANONYMOUS_CREDENTIALS = new AWSStaticCredentialsProvider(
+            new AnonymousAWSCredentials());
+    private static final String DUMMY_REGION = "us-west-1"; // Ignored because we use anonymous credentials
     private static final int TIME_OUT = 2000; // Milliseconds
     private XRayClient() {}
 
     public static AWSXRay newClient() {
         DaemonConfiguration config = new DaemonConfiguration();
 
         ClientConfiguration clientConfig = new ClientConfiguration()
-                .withSignerOverride(SignerFactory.NO_OP_SIGNER)
                 .withRequestTimeout(TIME_OUT);
 
         AwsClientBuilder.EndpointConfiguration endpointConfig = new AwsClientBuilder.EndpointConfiguration(
@@ -28,6 +31,7 @@ public static AWSXRay newClient() {
         return AWSXRayClientBuilder.standard()
                 .withEndpointConfiguration(endpointConfig)
                 .withClientConfiguration(clientConfig)
+                .withCredentials(ANONYMOUS_CREDENTIALS) // This will entirely skip signing too
                 .build();
 
     }