download() is not CI log friendly

[AndreMiras]

The way we report download progress in buildozer/__init__.py download() is absolutely helpful in the terminal, but really messes up with Travis logger.

When downloading things as big as the Android NDK via buildozer, it produces a very large amount of progress lines, like in the extract below:

�[0m�[1;34m# Android NDK is missing, downloading�[0m
- Download 0.00%
- Download 0.00%
- Download 0.00%
- Download 0.00%
- Download 0.00%
- Download 0.01%
- Download 0.01%
- Download 0.01%
- Download 0.01%
- Download 0.01%
- Download 0.01%
- Download 0.01%
- Download 0.01%
- Download 0.02%
- Download 0.02%
- Download 0.02%

In total this log file has over 100K lines of - Download ! See attached screenshot and complete log for reference: https://api.travis-ci.org/v3/job/491113892/log.txt

To fix the issue, maybe we should make it possible to reduce the verbosity of this download() method. Other suggestions are very welcome.
Side note: same issue exists in p4a via download_file(), but the most annoying currently is buildozer as it generates lager downloads so far.

[mkg20001]

My fork, which includes this commit has an environment flag called CI_MODE which can be set to 1 to disable progress-printing

[AndreMiras]

Very nice, yes that's the idea 👍

[mkg20001]

Created PRs #833 and kivy/python-for-android#1727 that implement this. Hope this gets merged soon, then I can finally drop my forks of this project