scripts/get_archive, tools-distro-tool: fix wget redirection issue when wget running in background

[MilhouseVH]

Issue discussed here, although doesn't actually resolve it as latest 1.19.5 still has the same issue, in which case I'm not sure if this is a regression/bug in wget or new/expected behaviour.

To reproduce:

1. Create /tmp/test.sh

#!/bin/bash

wget --timeout=30 --tries=3 --passive-ftp --no-check-certificate -c -O /tmp/aom.tar.gz "http://repo.or.cz/aom.git/snapshot/1b0e7dc4ac4b50f245dacc1e2362e50b7b2d1860.tar.gz"

2. Run /tmp/test.sh as a "background" process

bash /tmp/test.sh &

Result: instead of the output from wget being sent to the console, it is sent instead to wget-log in the current directory. And if wget-log exists, then wget-log.1 is created, then wget-log.2 etc. etc.

Adding --output-file=- overrides the buggy/new behaviour whenever wget is being run in the background.

Edit to add OS details:

Ubuntu 16.04 with wget 1.17.1: wget output always appears in the console regardless of whether wget is a foreground or background process.

Ubuntu 17.10 with wget 1.19.1 (and presumably later): wget output appears in the console when wget is a foreground process, but is redirected to wget-log when a background process.