UK grocery giant Sainsbury's is to trial a new format at six sites under a redesigned "Sainsbury's savacentre" fascia. The first store, with a more simplified look, opens tomorrow [Thursday] in Northfield, Birmingham.   Under a "Making Life Taste Better For Less" strap line, the stores are designed to deliver a stronger emphasis on value. The new Sainsbury's savacentres also aim to attract family shoppers, stocking the full range of Sainsbury's Economy products, the best selling products from other ranges such as Taste the Difference and many new, family sized, food products.