Fix flatpak build on atomic
Fix flatpak build on atomic

On atomic, /home is a symlink to /var/home, which caused
problems in flatpak build when granting access to the homedir.
Due to a previous workaround (in 1aadc3ee40f915927c129d0090d95497a23b4f5f) we
make /var in the flatpak build sandbox be completely overridden
with $builddir/var so that the above symlink would not cause problems
in the persisted directory.

However, when we actually *want* to give access to that symlink this
causes problem.

In general, exposing /var in the sandbox has two uses:

 * Allowing persisting tmpfiles in /var/tmp between individual
   flatpak build commands (/tmp is per-build-command).
 * Creating flatpaks from packages, such as rpms, where
   we want to keep the rpm database (/var/lib/rpm) around during
   the entire build so that dependencies can be resolved.

In order to handle these /var/home issues while still allowing
the above issues we instead persist only /var/tmp and /var/lib.

Fixes https://github.com/flatpak/flatpak/issues/1407

Closes: #1421
Approved by: alexlarsson

matthiasclasen/flatpak,flatpak/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,flatpak/flatpak,flatpak/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,matthiasclasen/flatpak,handsome-feng/flatpak,flatpak/flatpak,flatpak/flatpak,handsome-feng/flatpak