scripts: use git archive in archive-source

scripts: use git archive in archive-source

Use git archive to create tarballs of qemu and submodules instead of
cloning the repository and the submodules.  This is a order of magnitude
faster because it doesn't fetch the submodules from the internet each
time the script runs.

Signed-off-by: Gerd Hoffmann <[email protected]>
Tested-by: Thomas Huth <[email protected]>
Tested-by: Philippe Mathieu-Daudé <[email protected]>
Message-Id: <20190520124716[email protected]>
[AJB: fixed up tabs]
Signed-off-by: Alex Bennée <[email protected]>