support/docker: don't be silent when setting up

This image is not built very often, and when it is, it is important to
see what's going on, so don't be silent when installing packages from
the distro, and since that can take a bit of time it thus serves as
progress report...

Signed-off-by: "Yann E. MORIN" <yann.morin.1998@free.fr>
Cc: Arnout Vandecappelle <arnout@mind.be>
Signed-off-by: Peter Korsgaard <peter@korsgaard.com>