tests: Fix sporadic failure of TestXLStorageDeleteFile (#14911)

The test expects from DeleteFile to return errDiskNotFound when the disk
is not available. It calls os.RemoveAll() to remove one disk after XL storage
initialization. However, this latter contains some goroutines which can
race with os.RemoveAll() and then the test fails sporadically with
returning random errors.

The commit will tweak the initialization routine of the XL storage to
only run deletion of temporary and metacache data in the  background,
so TestXLStorageDeleteFile won't fail anymore.

cmd/prepare-storage.go

@@ -70,7 +70,7 @@ var printEndpointError = func() func(Endpoint, error, bool) {
 }()
 
 // Cleans up tmp directory of the local disk.
-func formatErasureCleanupTmp(diskPath string) {
+func bgFormatErasureCleanupTmp(diskPath string) {
 	// Need to move temporary objects left behind from previous run of minio
 	// server to a unique directory under `minioMetaTmpBucket-old` to clean
 	// up `minioMetaTmpBucket` for the current run.
@@ -98,9 +98,8 @@ func formatErasureCleanupTmp(diskPath string) {
 	}
 
 	go removeAll(tmpOld)
-
 	// Renames and schedules for purging all bucket metacache.
-	renameAllBucketMetacache(diskPath)
+	go renameAllBucketMetacache(diskPath)
 }
 
 // Following error message is added to fix a regression in release