* Ukraine plans to boost gas imports from Europe * Has failed to renegotiate long-term contract with Russia * LNG and Turkmen imports less feasible - analyst By Olzhas Auyezov KIEV, Feb 26 (Reuters) - Ukraine wants to import up to 8 billion cubic metres of gas a year from central Europe to replace expensive Russian supplies and take advantage of lower prices on the European spot market, a senior energy official said on Tuesday.