Keep compute nodes off when power comes back

When the power comes back, we don't know if the AC unit will be
operating properly or if the room will be at a safe temperature. So,
instead of powering all the machines back, only configure the login to
power on, so we can check the state of the room and power the rest of
the machines.

m/common/base.nix

@@ -3,7 +3,6 @@
   # Includes the basic configuration for an Intel server.
   imports = [
     ./base/agenix.nix
-    ./base/always-power-on.nix
     ./base/august-shutdown.nix
     ./base/boot.nix
     ./base/env.nix
@@ -12,6 +11,7 @@
     ./base/net.nix
     ./base/nix.nix
     ./base/ntp.nix
+    ./base/power-policy.nix
     ./base/rev.nix
     ./base/ssh.nix
     ./base/users.nix