BOSTON (Reuters) - Democratic Rep. Stephen Lynch, a former ironworker, on Thursday officially launched a bid for U.S. Senate, seeking the seat being vacated by John Kerry who was confirmed this week as the new U.S. Secretary of State. Lynch will face off against fellow House member Edward Markey in an April 30 primary ahead of a June 25 special election to choose a permanent successor to Kerry. In an online video, Lynch's campaign gives a broad-brush biography of the former ironworker, who grew up in public housing and ran a local union before going into politics. ...