makebuildserver: stop trying to write to Vagrantfile.yaml
makebuildserver: stop trying to write to Vagrantfile.yaml

If Vagrantfile.yaml exists, makebuildserver should no longer try to write
to it.  It is now manully managed now that makebuildserver.config.py no
longer exists.  Also, now that the buildserver is smaller, the workflow is
to always destroy and recreate it rather than ever try to reprovision it.

f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver,f-droid/fdroidserver