Fix mesos_zk_url: unbound variable.
Fix mesos_zk_url: unbound variable.

Capgemini/Apollo,atsaki/Apollo,ravbaba/Apollo,mehulsbhatt/Apollo,siliconmeadow/Apollo,Capgemini/Apollo,Capgemini/Apollo,siliconmeadow/Apollo,enxebre/Apollo,atsaki/Apollo,phungmanhcuong/Appolo,enxebre/Apollo,phungmanhcuong/Appolo,mehulsbhatt/Apollo,ravbaba/Apollo