[BUG: #237] roots/etc/monit.d: add cron to be monitored by monit

Signed-off-by: Adam Wujek <dev_public@wujek.eu>

userspace/rootfs_override/etc/monit.d/cron.conf

+check process crond matching /usr/sbin/crond
+   start program = "/etc/init.d/cron.sh start"
+   stop program = "/etc/init.d/cron.sh stop"
+   if 5 restarts within 10 cycles then exec "/etc/init.d/reboot.sh crond"