Update tar write function to skip irregular file

This resolves the occassional 'archive/tar: write too long' error

Signed-off-by: Ivan Sim <isim@redhat.com>

core/cmd/main.go

@@ -197,15 +197,14 @@ func compressed(dataDir string, blocks []*promtsdb.Block, writer *io.PipeWriter)
 				return err
 			}
 
-			// if dir, only write header
-			if info.IsDir() {
-				return writeHeader(path, info, tar.TypeDir)
-			}
-
 			if err := writeHeader(path, info, tar.TypeReg); err != nil {
 				return err
 			}
 
+			if !info.Mode().IsRegular() {
+				return nil
+			}
+
 			data, err := ioutil.ReadFile(path)
 			if err != nil {
 				return fmt.Errorf("failed to read data file: %w", err)