chore: Finish up install scripts.

nixinfra/update.sh

@@ -0,0 +1,16 @@
+#!/usr/bin/env bash
+if [[ "$NIX_BUILD_ID" == "" ]]; then
+  echo "ERROR: You have held a (potentially) broken install!"
+  echo "NIX_BUILD_ID is not set (should be set by default!)"
+  echo "Please set NIX_BUILD_ID manually. i.e:"
+  echo "NIX_BUILD_ID=kitteh-node-1/agent updater"
+  exit 1
+fi
+
+if [[ "$UID" != "0" ]]; then
+  sudo $0 $@
+  exit $?
+fi
+
+export NIX_PATH="$(printf $NIX_PATH | sed --expression="s#/etc/nixos/configuration.nix#/etc/nixos/nixinfra/$NIX_BUILD_ID.nix#g")"
+nixos-rebuild switch --upgrade