server: Add more elaborate startup messages. (#2731)

These messages based on our prep stage during XL
and prints more informative message regarding
drive information.

This change also does a much needed refactoring.

cmd/namespace-lock_test.go

@@ -301,11 +301,6 @@ func TestLockStats(t *testing.T) {
 	// initializing the locks.
 	initNSLock(false)
 
-	// set debug lock info  to `nil` so that the next tests have to initialize them again.
-	defer func() {
-		nsMutex.debugLockMap = nil
-	}()
-
 	// hold 10 read locks.
 	for i := 0; i < 10; i++ {
 		nsMutex.RLock("my-bucket", "my-object", strconv.Itoa(i))