Move onboot startup script to runc package

As this does not use containerd at all, this means you can run very
minimal setups with just `runc` if you use no services, for example
most of our tests do not actually use services, or if you have other
similar very minimal use cases.

Move ulimit setup to `init` which makes more sense.

Signed-off-by: Justin Cormack <justin.cormack@docker.com>

pkg/init/bin/rc.init

@@ -114,6 +114,10 @@ mount --make-rshared /var
 # make / rshared
 mount --make-rshared /
 
+# set global ulimits TODO move to /etc/limits.conf?
+ulimit -n 1048576
+ulimit -p unlimited
+
 # execute other init processes
 INITS="$(find /etc/init.d -type f | sort)"
 for f in $INITS