VMware: optimize in get_cluster_refs
VMware: optimize in get_cluster_refs

In get_cluster_refs method, for the sake of getting cluster names
references, there are two for loop sentences.

This patch merges into one for loop. (Trivial fix)

Change-Id: Ib7dfbe0294a5ee7988a18adfbf59159c2b6641e4

phenoxim/cinder,dims/cinder,bswartz/cinder,Nexenta/cinder,j-griffith/cinder,eharney/cinder,mahak/cinder,cloudbase/cinder,NetApp/cinder,ge0rgi/cinder,mahak/cinder,dims/cinder,j-griffith/cinder,phenoxim/cinder,Hybrid-Cloud/cinder,Datera/cinder,openstack/cinder,Hybrid-Cloud/cinder,NetApp/cinder,bswartz/cinder,cloudbase/cinder,openstack/cinder,Nexenta/cinder,Datera/cinder,eharney/cinder