Bug#857374: virtualenvwrapper: bash completion lacks testing for availability

[ydirson]

Package: virtualenvwrapper
Version: 4.3.1-2

When virtualenvwrapper is uninstalled but not purged, we get this each time 
bash completion is sourced:

bash: /usr/share/virtualenvwrapper/virtualenvwrapper_lazy.sh: No such file or 
directory