* Eight banks to arrange roadshows from Jan. 8* Perpetual dollar Tier 1 sukuk may follow* CEO said DIB needed capital boost after strong growth* Likely first Gulf bond deal of 2015By Archana NarayananDUBAI, Jan 7 (Reuters) - Dubai Islamic Bank DISB.DU will reopen the Gulf bond market next week with a capital-boosting sukuk, the region&aposs first debt offering in two months as financial markets th