A bevy of big shots turned up at the Boston Harbor Hotel Tuesday to welcome Fiach Mac Conghail, director of Dublin’s famed Abbey Theatre, in advance of the Abbey’s production of “The Plough and the Stars’’ at the American Repertory Theater in September. Tom O’Neill, who chairs the Abbey’s Boston chapter, BostonCoach’s Larry Moulter, arts patron Ted Cutler, Ireland’s consul general Fionnuala Quinlan, Pyramid Hotel Group CEO Richard Kelleher, Boston’s arts chief Julie Burros, and Mayor Marty Walsh were all present as Mac Conghail said it was only natural to stage Sean O’Casey’s play about the 1916 Easter Rising during the centenary of the famous rebellion. Walsh, who’s been linked to a grand jury investigation into labor union tactics, recalled that one of the Rising’s leaders, James Connolly, lived briefly in Mission Hill and worked in Boston as “a union organizer when it wasn’t a bad thing to be a union organizer.’’ The crack got an enthusiastic response from the friendly crowd. Mac Conghail, who gave Walsh a framed copy of the Abbey’s Manifesto, written by William Butler Yeats, said the Abbey will team up with the Boston Public Library for some special programming.