We should detect when the lpadmin command fails and keep track of the printers we have successfully added so that we only remove those during cleanup.
This is an issue because if the same printer is plugged into 2 computers, each may have the same definition and since we don't add a prefix to the forwarded printer name, we will try to add the same name - which fails, but then we end up deleting the printer we did not create.
The first hurdle is that the reaper code somehow makes python unaware of the actual returncode from the lpadmin command, r10119 fixes that (should backport too).
r10120 takes care of not registering printers until the lpadmin command returns success (returncode=0). A bit too big for backports, maybe later. (so keeping the ticket open)
Not backporting it because it is too big, focusing on getting 0.16 finished instead.
See also #2095
this ticket has been moved to: https://github.com/Xpra-org/xpra/issues/930