update to aws-sdk-go v1.16.15

vendor/github.com/aws/aws-sdk-go/internal/shareddefaults/ecs_container.go

@@ -0,0 +1,12 @@
+package shareddefaults
+
+const (
+	// ECSCredsProviderEnvVar is an environmental variable key used to
+	// determine which path needs to be hit.
+	ECSCredsProviderEnvVar = "AWS_CONTAINER_CREDENTIALS_RELATIVE_URI"
+)
+
+// ECSContainerCredentialsURI is the endpoint to retrieve container
+// credentials. This can be overridden to test to ensure the credential process
+// is behaving correctly.
+var ECSContainerCredentialsURI = "http://169.254.170.2"