CLOUDSTACK-7360 [vmware] Add host to existing cluster fails if the cluster is using Nexus 1000v as backend for atleast one traffic type.

While adding host to existing cluster which is using Nexus 1000v as a network backend, skip validation of Nexus VSM as it was already done while adding that cluster.

Signed-off-by: Sateesh Chodapuneedi <sateesh@apache.org>