(Reuters) – U.S. cybersecurity firm NortonLifeLock Inc on Thursday delayed the expected completion date for its buyout of London-listed rival Avast Plc to April 4, saying it was awaiting regulatory nods in the United Kingdom and Spain. The cash-and-stock deal, valued at up to $8.6 billion when it was first announced in August last year, was earlier expected to close on Feb. 24. NortonLifeLock’s shares were down 2.1% in extended trading. The takeover has attracted the scrutiny of Britain’s competition regulator and the agency in January launched an investigation into whether the deal will reduc…