mirror: Stop minio-go bucket listen when watch is cancelled (#4053)
mirror: Stop minio-go bucket listen when watch is cancelled (#4053)

When mirror in --watch mode is restarted, the previous minio-go
ListenNotification/ListenBucketNotification call is not properly
canceled. This commit creates a new context for that listen call and
cancels it when client-s3 Watch() is asked to be stopped.

vadmeste/mc,vadmeste/mc,krisis/mc,krisis/mc,minio/mc,minio/mc,balamurugana/mc,balamurugana/mc