objectLayer: Check for format.json in a wrapped disk. (#3311)

This is needed to validate if the `format.json` indeed exists
when a fresh node is brought online.

This wrapped implementation also connects to the remote node
by attempting a re-login. Subsequently after a successful
connect `format.json` is validated as well.

Fixes #3207

cmd/posix.go

@@ -193,6 +193,16 @@ func (s *posix) String() string {
 	return s.diskPath
 }
 
+// Init - this is a dummy call.
+func (s *posix) Init() error {
+	return nil
+}
+
+// Close - this is a dummy call.
+func (s *posix) Close() error {
+	return nil
+}
+
 // DiskInfo provides current information about disk space usage,
 // total free inodes and underlying filesystem.
 func (s *posix) DiskInfo() (info disk.Info, err error) {