fix: New disks healing should pick unformatted disks as well (#13054)

A recent regression caused new disks not being re-formatted. In the old
code, a disk needed be 'online' to be chosen to be formatted but the
disk has to be already formatted for XL storage IsOnline() function to
return true.

It is enough to check if XL storage is nil or not if we want to avoid
formatting root disks.

Co-authored-by: Anis Elleuch <anis@min.io>

.github/workflows/go.yml

@@ -32,3 +32,4 @@ jobs:
           sudo sysctl net.ipv6.conf.all.disable_ipv6=0
           sudo sysctl net.ipv6.conf.default.disable_ipv6=0
           make verify
+          make verify-healing

cmd/format-erasure.go

@@ -705,7 +705,7 @@ func saveUnformattedFormat(ctx context.Context, storageDisks []StorageAPI, forma
 		if format == nil {
 			continue
 		}
-		if storageDisks[index] != nil && storageDisks[index].IsOnline() {
+		if storageDisks[index] != nil {
 			if err := saveFormatErasure(storageDisks[index], format, true); err != nil {
 				return err
 			}