Lxd rsync live migration error

@stgraber If I revert the following commit it works again:

commit 7dfc2939ac278d8436ff4b892599c795c5482007
Author: Stéphane Graber stgraber@ubuntu.com
Date: Thu Aug 23 19:27:31 2018 -0400

global: Advertise rsync features

Closes #4962

Somehow the pre-dump loop seems to have problems with the additional information on the channel.