cmd/geth, metrics: separate process metric collection, add disk

metrics/disk.go

@@ -0,0 +1,9 @@
+package metrics
+
+// DiskStats is the per process disk io stats.
+type DiskStats struct {
+	ReadCount  int64 // Number of read operations executed
+	ReadBytes  int64 // Total number of bytes read
+	WriteCount int64 // Number of write operations executed
+	WriteBytes int64 // Total number of byte written
+}