Add structured log messages to Geo LogCursor
Adds log messages such as the following:
{"severity":"INFO","time":"2017-08-02T05:26:03.950Z","class":"Gitlab::Geo::LogCursor::Daemon","message":"Repository update","cursor_delay_s":20.166,"project_id":8,"source":"repository","resync_repository":true,"resync_wiki":false}
Edited by Stan Hu