Currently it is not possible to create a volume within the UI. The UI still shows the new created volume, but in real the volume is not created if you check that via lvs in the CLI.
To fix that the API_OS_USER variable in backend/settings.py must be modified to 'vagrant'.
Additionally it is necessary to symlink the blkdevzero command to /bin.
Finally it is necessary to replace the hardcoded 'openattic' owner in FileSystem::configure_blockvolume (see backend/volumes/filesystems/filesystem.py) to API_OS_USER or something else to get this code running in a Vagrant box, too.