refactor: modularize utils

utils/hosts.nix

@@ -0,0 +1,8 @@
+{
+  hostMeta =
+    hostDir:
+    if builtins.pathExists (hostDir + "/meta.nix") then
+      import (hostDir + "/meta.nix")
+    else
+      throw "meta.nix required in ${hostDir}";
+}