On open repository open common cat file batch and batch-check (#15667)

Use common git cat-file --batch and git cat-file --batch-check to
significantly reduce calls to git.
    
Signed-off-by: Andrew Thornton <art27@cantab.net>

modules/git/repo_blob_test.go

@@ -33,9 +33,9 @@ func TestRepository_GetBlob_Found(t *testing.T) {
 
 		dataReader, err := blob.DataAsync()
 		assert.NoError(t, err)
-		defer dataReader.Close()
 
 		data, err := ioutil.ReadAll(dataReader)
+		assert.NoError(t, dataReader.Close())
 		assert.NoError(t, err)
 		assert.Equal(t, testCase.Data, data)
 	}