By Vitalii Hnidyi and Thomas Peter NEAR KUPIANSK, Ukraine (Reuters) – Rows of white concrete barricades and coils of razor wire stretch across an open field for more than a kilometre. Trenches with rudimentary living quarters are being dug under cover of darkness. Artillery rumbles not far away. New defensive lines visited by Reuters near the northeastern city of Kupiansk on Dec. 28 show how Ukraine has stepped up construction of fortifications in recent months as it shifts its military operations against Russia to a more defensive footing. The defences, which bear some similarities to those r…