gmetad: include sources without data sources in summaryzation
gmetad: include sources without data sources in summaryzation

affecting the root summary in an multi level gmetad setup as
reported by Tymothy Witham


lawrencewu/monitor-core,NoodlesNZ/monitor-core,torkelsson/monitor-core,torkelsson/monitor-core,fastly/monitor-core,torkelsson/monitor-core,ganglia/monitor-core,NoodlesNZ/monitor-core,lawrencewu/monitor-core,phreakocious/monitor-core,fastly/monitor-core,mjzhou/monitor-core,hinesmr/monitor-core,sdgdsffdsfff/monitor-core,dmourati/monitor-core,NoodlesNZ/monitor-core,mjzhou/monitor-core,torkelsson/monitor-core,dmourati/monitor-core,dmourati/monitor-core,lawrencewu/monitor-core,NoodlesNZ/monitor-core,dmourati/monitor-core,ganglia/monitor-core,phreakocious/monitor-core,fastly/monitor-core,ganglia/monitor-core,NoodlesNZ/monitor-core,torkelsson/monitor-core,mjzhou/monitor-core,sdgdsffdsfff/monitor-core,sdgdsffdsfff/monitor-core,phreakocious/monitor-core,hinesmr/monitor-core,lawrencewu/monitor-core,fastly/monitor-core,ganglia/monitor-core,hinesmr/monitor-core,fastly/monitor-core,mjzhou/monitor-core,torkelsson/monitor-core,ganglia/monitor-core,sdgdsffdsfff/monitor-core,mjzhou/monitor-core,dmourati/monitor-core,mjzhou/monitor-core,phreakocious/monitor-core,ganglia/monitor-core,phreakocious/monitor-core,hinesmr/monitor-core,sdgdsffdsfff/monitor-core,NoodlesNZ/monitor-core,mjzhou/monitor-core,hinesmr/monitor-core,fastly/monitor-core,lawrencewu/monitor-core,fastly/monitor-core,NoodlesNZ/monitor-core,lawrencewu/monitor-core,phreakocious/monitor-core,ganglia/monitor-core,dmourati/monitor-core,ganglia/monitor-core,torkelsson/monitor-core,sdgdsffdsfff/monitor-core,phreakocious/monitor-core,lawrencewu/monitor-core,sdgdsffdsfff/monitor-core