convert mount service to trigger

Good: this means it's not hanging holding the s6 dataase lock.

Bad: it's the ugliest implementation and doesn't deserve to be preserved

(tbf the ugliness is not new)

tests/ci.nix

@@ -9,4 +9,5 @@
   fennel = import ./fennel/test.nix;
   tftpboot = import ./tftpboot/test.nix;
   updown = import ./updown/test.nix;
+  inout = import ./inout/test.nix;
 }