By Henriette Chacar and Nisreen Salem JERUSALEM (Reuters) – A few steps from Jerusalem’s Church of the Holy Sepulchre, a small opening leads to an underground cistern where clerics have found the perfect place to practise chants ahead of the holiest day in the Christian calendar. As Eastern churches prepared to mark Easter one week after the Roman Catholic celebration, Barakat al-Masri stood deep underneath Saint Helena’s Coptic Orthodox church, chanting hymns in Coptic and Arabic. The cistern is not much to look at, but al-Masri, the cantor at the Coptic church, says the sound it produces is …