bitrot: add selftest for server startup (#11917)

This commit adds a self-test for all bitrot algorithms:
 - SHA-256
 - BLAKE2b
 - HighwayHash

The self-test computes an incremental checksum of pseudo-random
messages. If a bitrot algorithm implementation stops working on
some CPU architecture or with a certain Go version this self-test
will prevent the server from starting and silently corrupting data.

For additional context see: minio/highwayhash#19

cmd/server-main.go

@@ -413,6 +413,7 @@ func serverMain(ctx *cli.Context) {
 	logger.AddTarget(globalConsoleSys)
 
 	// Perform any self-tests
+	bitrotSelfTest()
 	erasureSelfTest()
 	compressSelfTest()