jenkins: force local basebox, do not download from Vagrant Cloud
jenkins: force local basebox, do not download from Vagrant Cloud

Until we have a verification process for boxes downloaded from Vagrant
Cloud, the official setup uses a locally generated basebox.

f-droid/fdroid-server,f-droid/fdroidserver,f-droid/fdroidserver,fdroidtravis/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroid-server,f-droid/fdroid-server,f-droid/fdroidserver,fdroidtravis/fdroidserver,f-droid/fdroid-server,fdroidtravis/fdroidserver,f-droid/fdroid-server