Fix watching multiple Zookeeper paths in serverset SD.
Fix watching multiple Zookeeper paths in serverset SD.

Fix https://github.com/prometheus/prometheus/issues/1137

agaoglu/prometheus,tattsun/prometheus,mtanda/prometheus,datajet-io/prometheus,agaoglu/prometheus,PrFalken/prometheus,Conorbro/prometheus,SaltedMan/prometheus-annotated,keegancsmith/prometheus,GoogleCloudPlatform/prometheus,gottwald/prometheus,Stackdriver/stackdriver-prometheus,AlekSi/prometheus,msiebuhr/prometheus,GoogleCloudPlatform/prometheus,AlekSi/prometheus,datajet-io/prometheus,kzittritsch/prometheus,alileza/prometheus,wrouesnel/prometheus,ton31337/prometheus,Colstuwjx/prometheus,tomwilkie/prometheus,wrouesnel/prometheus,iksaif/prometheus,JavierZunzunegui/prometheus,Colstuwjx/prometheus,msiebuhr/prometheus,JavierZunzunegui/prometheus,slok/prometheus,Stackdriver/stackdriver-prometheus,Conorbro/prometheus,slok/prometheus,brancz/prometheus,GoogleCloudPlatform/prometheus,Stackdriver/stackdriver-prometheus,yanghongkjxy/prometheus,yanghongkjxy/prometheus,sudhi-vm/prometheus,kangwoo/prometheus,sudhi-vm/prometheus,alileza/prometheus,keegancsmith/prometheus,brancz/prometheus,sudhi-vm/prometheus,mtanda/prometheus,JavierZunzunegui/prometheus,yanghongkjxy/prometheus,kangwoo/prometheus,prometheus/prometheus,datajet-io/prometheus,yanghongkjxy/prometheus,adamron1/prometheus,Stackdriver/stackdriver-prometheus,keegancsmith/prometheus,iksaif/prometheus,tomwilkie/prometheus,amorken/prometheus,iksaif/prometheus,Colstuwjx/prometheus,PrFalken/prometheus,dsymonds/prometheus,agaoglu/prometheus,Gouthamve/prometheus,Conorbro/prometheus,agaoglu/prometheus,gottwald/prometheus,Colstuwjx/prometheus,PrFalken/prometheus,thachmai/prometheus,prometheus/prometheus,brancz/prometheus,dsymonds/prometheus,adamron1/prometheus,amorken/prometheus,tomwilkie/prometheus,eliothedeman/prometheus,wrouesnel/prometheus,keegancsmith/prometheus,dmilstein/prometheus,SaltedMan/prometheus-annotated,prometheus/prometheus,Gouthamve/prometheus,SaltedMan/prometheus-annotated,datajet-io/prometheus,Conorbro/prometheus,msiebuhr/prometheus,dsymonds/prometheus,dmilstein/prometheus,slok/prometheus,thachmai/prometheus,msiebuhr/prometheus,thachmai/prometheus,alileza/prometheus,thachmai/prometheus,gottwald/prometheus,alileza/prometheus,adamron1/prometheus,kangwoo/prometheus,mtanda/prometheus,iksaif/prometheus,slok/prometheus,kzittritsch/prometheus,GoogleCloudPlatform/prometheus,Gouthamve/prometheus,keegancsmith/prometheus,brancz/prometheus,tattsun/prometheus,amorken/prometheus,dmilstein/prometheus,Gouthamve/prometheus,eliothedeman/prometheus,ton31337/prometheus,mtanda/prometheus,AlekSi/prometheus,GoogleCloudPlatform/prometheus,wrouesnel/prometheus,tattsun/prometheus,kangwoo/prometheus,tattsun/prometheus,kzittritsch/prometheus,kzittritsch/prometheus,SaltedMan/prometheus-annotated,PrFalken/prometheus,adamron1/prometheus,AlekSi/prometheus,amorken/prometheus,tomwilkie/prometheus,JavierZunzunegui/prometheus,dmilstein/prometheus,eliothedeman/prometheus,ton31337/prometheus,sudhi-vm/prometheus,prometheus/prometheus,gottwald/prometheus,ton31337/prometheus,alileza/prometheus,dsymonds/prometheus,prometheus/prometheus,eliothedeman/prometheus