[INTERNAL] deprecated Saros#Resource string

Building a fully qualified JID with this resource string may fail very
badly.

Change-Id: Ibe680bfe7171380e07c1de52beea303ce0d0b02e
Reviewed-on: http://saros-build.imp.fu-berlin.de/gerrit/1450
Tested-by: Jenkins CI
Reviewed-by: Stefan Rossbach <srossbach@arcor.de>