Fix the empty machines

Among other things, https://whetstone.privatestorage.io/opensource/PrivateStorageio/-/merge_requests/72 shuffles around the way morph refers to machines in the deployment a little. This was not strictly necessary and I should have known better!

These changes tickle https://github.com/DBCDK/morph/issues/77 which cause morph to empty a completely empty network for the grid. Joy.

This MR updates our nixpkgs to a version with two changes:

• The incompatibility between morph >=1.3.1 and NixOS AWS support has been mitigated with a change to the nixpkgs definitions for AWS EC2 support (https://github.com/PrivateStorageio/nixpkgs/commit/b8240ab9525aaab8f8587e8aaf7be99fcca5c220)
• Morph has been upgraded to 1.4.0 which includes a fix for the bug that results in an empty network (https://github.com/PrivateStorageio/nixpkgs/compare/c54e4650cadc90152a345e070d7036cdda3aae8e..d7c46f46c3e6acfcde44bb05877fd5c9f07dfe1b)

nixpkgs.json

 { "name": "nixpkgs"
-, "url": "https://github.com/PrivateStorageio/nixpkgs/archive/31c7a57bd9972979275fbfd9e490bfb502154c11.tar.gz"
-, "sha256": "0chvfxi2xcqhnabivjych8xdz7lm9svkvribjssyyaxc54xpql24"
+, "url": "https://github.com/PrivateStorageio/nixpkgs/archive/d7c46f46c3e6acfcde44bb05877fd5c9f07dfe1b.tar.gz"
+, "sha256": "1vddxhp3ljaq9qqzbpjp2kx34ps7nzbsn4zy31x0748a52rlsh0q"
 }