Set power policy to always turn on

In all machines, as soon as we recover the power, turn the machine back
on. We cannot rely on the previous state as we will shut them down
before the power is cut to prevent damage on the power supply
monitoring circuit.

m/common/base.nix

@@ -3,6 +3,7 @@
   # 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

m/common/base/always-power-on.nix

@@ -0,0 +1,8 @@
+{
+  imports = [
+    ../../module/power-policy.nix
+  ];
+
+  # Turn on as soon as we have power
+  power.policy = "always-on";
+}