Log x-amz-request-id as log and XML error response (#6173)

Currently, requestid field in logEntry is not populated, as the
requestid field gets set at the very end.
It is now set before regular handler functions. This is also
useful in setting it as part of the XML error response.

Travis build for ppc64le has been quite inconsistent and stays queued
for most of the time. Removing this build as part of Travis.yml for
the time being.

cmd/generic-handlers.go

@@ -723,6 +723,26 @@ func (l rateLimit) ServeHTTP(w http.ResponseWriter, r *http.Request) {
 	l.handler.ServeHTTP(w, r)
 }
 
+// requestIDHeaderHandler sets x-amz-request-id header.
+// Previously, this value was set right before a response
+// was sent to the client.So, logger and Error response XML
+// were not using this value.
+// This is set here so that this header can be logged as
+// part of the log entry and Error response XML.
+type requestIDHeaderHandler struct {
+	handler http.Handler
+}
+
+func addrequestIDHeader(h http.Handler) http.Handler {
+	return requestIDHeaderHandler{handler: h}
+}
+
+func (s requestIDHeaderHandler) ServeHTTP(w http.ResponseWriter, r *http.Request) {
+	// Set unique request ID for each response.
+	w.Header().Set(responseRequestIDKey, mustGetRequestID(UTCNow()))
+	s.handler.ServeHTTP(w, r)
+}
+
 type securityHeaderHandler struct {
 	handler http.Handler
 }