listObjects optimized to handle max-keys=1 when prefix is object (#13000)

Some applications albeit poorly written rather than using headObject
rely on listObjects to check for existence of object, this unusual
request always has prefix=(to actual object) and max-keys=1

handle this situation specially such that we can avoid readdir()
on the top level parent to avoid sorting and skipping, ensuring
that such type of listObjects() always behaves similar to a
headObject() call.

cmd/bootstrap-peer-server.go

@@ -188,7 +188,9 @@ func verifyServerSystemConfig(ctx context.Context, endpointServerPools EndpointS
 			// after 5 retries start logging that servers are not reachable yet
 			if retries >= 5 {
 				logger.Info(fmt.Sprintf("Waiting for atleast %d remote servers to be online for bootstrap check", len(clnts)/2))
-				logger.Info(fmt.Sprintf("Following servers are currently offline or unreachable %s", offlineEndpoints))
+				if len(offlineEndpoints) > 0 {
+					logger.Info(fmt.Sprintf("Following servers are currently offline or unreachable %s", offlineEndpoints))
+				}
 				retries = 0 // reset to log again after 5 retries.
 			}
 			offlineEndpoints = nil