pg_upgrade: Don't print progress status when output is not a tty.

pg_upgrade: Don't print progress status when output is not a tty.

Until this change pg_upgrade with output redirected to a file / pipe would end
up printing all files in the cluster. This has made check-world output
exceedingly verbose.

Author: Andres Freund <andres@anarazel.de>
Reviewed-By: Justin Pryzby <pryzby@telsasoft.com>
Reviewed-By: Daniel Gustafsson <daniel@yesql.se>
Discussion: https://postgr.es/m/CA+hUKGKjrV61ZVJ8OSag+3rKRmCZXPc03bDyWMqhXg3rdZ=fOw@mail.gmail.com