It will be at least eight years behind bars for the killer of a teenager in Norristown almost a year ago.   Nicholas Anthony Wiley was sentenced by a Montgomery County judge yesterday.   He pleaded guilty last August in connection with the third degree murder of Kyrie Swittenberg-Jenkins.   Wiley shot the victim outside a club in the West End of Norristown after a fight broke out.  Prosecutors say Wiley did not intend to kill Switttenberg-Jenkins but fired his gun into a crowd of teenagers with a reckless disregard for the consequences.   Another teenager was injured when the shots rang out.   Investigators also say the fight at the root of the incident was gang related.