Don't update system automatically

[ebknudsen]

It is not good practice to force system updates. This should not be done if dependencies can be met otherwise.
It creates a bad situation when dealing with cluster-nodes, where a build node might get out of sync with others.
(in a large-scale cluster situation easybuild is probably a better route.)

For debian, an example solution is to check for existing dependencies with apt but don't upgrade if not necessary.
Maybe a separate script for installing all dependencies if they're not there.

[ebknudsen]

for apt-get we should simply add the flag "--no-upgrade". That way already installed packages will not be upgraded, i..e. system will only be changed if necessary.

[ebknudsen]

similar for Arch, but some pther option for pacman is needed