kiji-schema: SCHEMA-837. Fix DebugResourceTracker logging message for double-registration

issue: https://jira.kiji.org/browse/SCHEMA-837
review: https://review.kiji.org/r/1957
over-the-shoulder-reviewers: ['ajprax']
commit: https://github.com/kijiproject/kiji-schema/commit/2affeab5714e51520cccfe74afb8246318c293b4