To access paths on the ESP before or after installing generations, split
EspPaths into general EspPaths that only depend on the path to the ESP
and EspGenerationPaths which additionally depend on generation specific
information (e.g. version number and initrd filename).
Add an extension to TempDir that allows to create secure tempfiles. This
way, everything related to creating secure tempfiles is bundled in a
single place and can easily be reused.
nikstur