Previously we already switch to loading the bootstrap file only from the
local file (ec42553910).
This removes the remaining parts of loading the bootstrap file from a
remote location.
This also updates the UI in case of parsing errors of the bootstrap.json.
This is an intermediate step to have smaller unit tests. It is a trade off
between having many many test executables compared to a few bigger ones. But
this comes a lot closer to what QtTest is meant to be used.
