* Use fully static build for the bootstrap daemon.
* Store a sha256sum of the binary in the repo.
* Updated documentation for it.
* Add support for fully static build in cmake.
* Enable the docker build on every PR, so we catch changes to the
checksum. I realise this is adding toil, but having the checksum is
valuable for security of released binaries.
Also, add an auto-test for bootstrap and for LAN discovery.
Bootstrap is never tested otherwise, and LAN discovery is a prerequisite
for everything else. Having these two tests lets us rule out or identify
LAN discovery as a possible cause for test failures.
