shell.nix: add random utilities

Change-Id: I49bfe400af054a8bcc0861f6066e7ca426590268
diff --git a/shell.nix b/shell.nix
index 3e0bdc4..1b504cf 100644
--- a/shell.nix
+++ b/shell.nix
@@ -25,6 +25,8 @@
     openldap.dev cyrus_sasl.dev # for python-ldap
     wkhtmltopdf
     gcc binutils
+    pwgen
+    tmate
   ];
   multiPkgs = pkgs: [
     (pkgs.runCommand "protocols" {}