charmhelpers.contrib.network.ip installs system packages when loaded

The contrib.network.ip module is installing system packages when loaded.

This means that the tests error if you don't have the package installed, and IMO is not a good idea generally.

I think it would be better to install these dependencies from a function inside the ip module, such as check_and_install_dependencies(). Call-sites using the ip module then have the responsibility to use the function.