Imporve healing and reporting (#11312)

* Provide information on *actively* healing, buckets healed/queued, objects healed/failed.
* Add concurrent healing of multiple sets (typically on startup).
* Add bucket level resume, so restarts will only heal non-healed buckets.
* Print summary after healing a disk is done.

cmd/storage-interface.go

@@ -36,7 +36,7 @@ type StorageAPI interface {
 	Close() error
 	GetDiskID() (string, error)
 	SetDiskID(id string)
-	Healing() bool // Returns if disk is healing.
+	Healing() *healingTracker // Returns nil if disk is not healing.
 
 	DiskInfo(ctx context.Context) (info DiskInfo, err error)
 	NSScanner(ctx context.Context, cache dataUsageCache) (dataUsageCache, error)
@@ -79,6 +79,9 @@ type StorageAPI interface {
 
 	// Read all.
 	ReadAll(ctx context.Context, volume string, path string) (buf []byte, err error)
+
+	GetDiskLoc() (poolIdx, setIdx, diskIdx int) // Retrieve location indexes.
+	SetDiskLoc(poolIdx, setIdx, diskIdx int)    // Set location indexes.
 }
 
 // storageReader is an io.Reader view of a disk