SEATTLE — It was a defensive background that Pete Carroll used to become the most successful coach in Seahawks history. And it is another coach with a defensive background — Mike Macdonald — who the Seahawks will count on to get them back to their Carroll-era glory years. After a morning of reports that the Seahawks had decided on Macdonald — the 36-year-old now former defensive coordinator of the Baltimore Ravens — as their new head coach, the team made it official with an announcement shortly after 4:30 p.m. Wednesday afternoon. Macdonald will be officially introduced at a press conference T…