By Amanda Ferguson BELFAST (Reuters) -Britain's prime minister told Northern Ireland politicians on Friday that progress had been made on easing post-Brexit trade rules as he sought to keep the province's sceptical unionists on side in a final push for a deal with the European Union. After weeks of intense London-Brussels talks, momentum has been building towards a deal to revise the Northern Ireland Protocol - the arrangements agreed to avoid a hard border with EU member Ireland when Britain exited the EU in 2020. "I had positive conversations with political parties in Northern Ireland," Prim...