Cardano Updates

Fix nix-shell CPU affinity

Fixing a deployment bug when pass is not available.

If you don't have `pass` available, or pointing to the right password
store, the error was silently being ignored and terraform would deploy
with any information we get from pass set to the empty string.

This fixes that issue.

It's disappointing to see that the heart of the fix comes from realising
that in bash:

    export FOO=$(command)

...will swallow an error, whereas:

    FOO=$(command)
    export FOO

...will throw it.

Adding some github debugging code.

This were lost in a recent reorganisation for AWS lambda, but they're
still useful.

A long time ago, Nikos pointed out to me that running the tests inside
`nix-shell` was much slower than outside it. I don't notice since I'm
using `lorri`, but this is quite annoying. I never figured out what the
issue was, it didn't seem to be environments or anything.

Someone else recently noticed something similar, and managed to  track it down
to a Nix bug where it sets the processor affinity wrong
(https://github.com/NixOS/nix/issues/3345). I didn't even know about
processor affinity! (Don't mutate global state while forking processes,
kids.)

The fix is a `shellHook` to put it back to something sensible, which
indeed gives us the behaviour we expect.