e709bc53

By: Tom Sydney Kerckhove <syd@cs-syd.eu>

Fail before the password when there is nowhere to write the record

Reading a router writes three files into the record directory, which is named
relative to wherever the command is run from. A command run from somewhere else
asked for a password, read the router, and only then said it could not write
the first file.

Also check in the one place every caller passes through, and assert the two
commands a deployment carries keep the shape this depends on: the one that
reads the router has to build for a configuration the checker refuses, because
that is the state somebody reaches for it in.