Trial starts today (Dec. 8) for a Florida policeman involved in the death almost a year ago of a black man whose killing eventually led to rioting in Miami last spring. The Justice Department chose San Antonio as the site of the civil rights trial of policeman Charles Veverka because of its apparently stable racial climate. The trial was moved here after being shifted from Tampa, Fla., to Atlanta, then New Orleans. Mr. Veverka is charged with violating the civil rights of Arthur McDuffie, a black insurance man. Although he received immunity at a trial in Tampa in which he and four other officers were acquitted by an all-white jury, he has been reindicted on federal charges.