[Tails-dev] Please review and merge tails-greeter:bugfix/69…

Please review and merge into tails-greeter:master
tails-greeter:bugfix/6959-persistent_printers.

I believe it fixes https://labs.riseup.net/code/issues/6959 "Persistence
of printer broken in Tails 0.23"

Please also merge bugfix/6959-persistent_printers-wheezy into
tails-greeter:wheezy

I'm too lazy to build a package and upload it to experimental for such
a tiny change. Dear RM, if you requires it just ask and I'll do it.

Cheers