init: switch to / after spawning subprocess

[cyphar]

Apparently podman runs catatonit -P in a subdirectory, pinning the mount. We probably need to spawn subprocesses in the directory we are run, but the directory of the init process shouldn't matter (and the vast majority of users would run us from / anyway).

Fixes #28 Signed-off-by: Aleksa Sarai [email protected]