pg_basebackup: Fix progress messages when writing to a file

The progress messages print out \r to keep overwriting the same line on
the screen.  But this does not yield useful results when writing the
output to a file.  So in that case, print out \n instead.

Author: Martín Marqués <martin@2ndquadrant.com>
Reviewed-by: Arthur Zakirov <a.zakirov@postgrespro.ru>