By Hyunjoo Jin SAN FRANCISCO (Reuters) -Fifteen Black former or current employees at Tesla filed a lawsuit against the electric car maker on Thursday, alleging they were subjected to racial abuse and harassment at its factories. The workers said they were subjected to offensive racist comments and behavior by colleagues, managers and human resources employees on a regular basis, according to the lawsuit filed in a California state court. The harassment, which occurred mostly at Tesla’s Fremont, California, factory, included using the n-word and such terms as “slavery” or “plantation” or making…