"debian/REQUIRED_PACKAGES" is used by gitlab-ci to prepare the image. We require
"udev" package, if only to install "/usr/share/pkgconfig/udev.pc" to get the
udev directory.
Otherwise build fails with:
Run-time dependency udev found: NO (tried pkgconfig)
meson.build:371:2: ERROR: Dependency "udev" not found, tried pkgconfig
On Ubuntu 16.04 (trusty) valgrind fails due to rdrand being advertised
but not implemented.
Work around that by installing valgrind from Ubuntu 18.04 (bionic) via
the "contrib/scripts/nm-ci-install-valgrind-in-ubuntu1604.sh" script.