Glibc provides /etc/nsswitch.conf but doesn't update it after first
install. This adds a check to ensure we have systemd dynamic support
present before running as we need dynamic users and a out of date
nsswitch overrides the up to date file in /usr/etc/ breaking support.
Cockpit expects all its users to be dynamic, if we aren't creating them
manually and instead using them as dynamic users as upstream expects we
need to ensure they don't exist. This adds a preexec script that does
that.