Upgrade Tahoe-LAFS on the storage servers

Re-importing the path probably breaks other stuff.  Anyway, we only have one
overlay now so this short/simpler thing works.

Rely on upstream package to supply typing and challenge-bypass-ristretto as
necessary.  Simplify our expression (approximately pointfree style) so we
don't have to know about any other arguments that might be passed or accepted.

Bump to branch that fixes the Copyable/ShareStat issue

Also adjust the system tests to account for the new authorization requirements.

Pin haskell.nix in LeaseReport

I don't know

When it changes we often have to rebuild ghc ... :(

Configure 1 SI MB pass value

Also configure a new value on the staging grid

Add LeaseReport to storage servers

Turn on Eliot logging on storage servers

Improved Tahoe-LAFS systemd unit ExecStartPre

This removes the code that might delete a Tahoe-LAFS nodedir and replaces it
with code that will try to save an unexpected copy of it out of the way
instead.