This commit makes check_cockpit_users only check for systemd dynamic
user support in nsswitch. We do not need to check for compat based on
what Thorsten Kukuk has said. Checking for arguments before systemd
maybe be problematic as for example usrfiles maybe present on some
hermetic-usr systems.
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present before running as we need dynamic users and a out of date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.
