Safe reboots

Add commands to safely reboot machines which are:

 * [safe to reboot](https://github.gds/pages/gds/opsmanual/2nd-line/rebooting-machines.html)
 * not a datastore such as mongo or elasticsearch
 * not a monitoring box which will cause alert confusion if rebooted
 * have the same number in their group
good catch, will fix.