ade: Append distro, release, and arch to sysroot file name

Currently the sysroot file is named 'sysroot'. This prevents to have
different latests sysroot for different architectures. For example, ade
sysroot latest --arch arm64 returns the url of the armhf sysroot if it
was the last sysroot uploaded.
A symbolic link called sysroot can be used so that older version of
ade are still able to download a sysroot file.

Apertis: https://phabricator.apertis.org/T3849



Signed-off-by: Frédéric Dalleau <frederic.dalleau@collabora.com>
Reviewed-by: Simon McVittie <smcv@collabora.com>
Differential Revision: https://phabricator.apertis.org/D6678