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/routers.go

@@ -47,6 +47,8 @@ func registerDistXLRouters(router *mux.Router, endpoints EndpointList) {
 
 // List of some generic handlers which are applied for all incoming requests.
 var globalHandlers = []HandlerFunc{
+	// set x-amz-request-id header.
+	addrequestIDHeader,
 	// set HTTP security headers such as Content-Security-Policy.
 	addSecurityHeaders,
 	// Forward path style requests to actual host in a bucket federated setup.