Accept CLUSTER attribute for new vnet and ds templates

[OpenNebulaProject]

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Author Name: Carlos Martín (Carlos Martín)
Original Redmine Issue: 2698, https://dev.opennebula.org/issues/2698
Original Date: 2014-01-30

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onevnet/datastore create accept the --cluster option, but since all the configuration is done with a template, we could also try to get the destination cluster from the template.

See http://lists.opennebula.org/pipermail/users-opennebula.org/2014-January/026358.html

[rsmontero]

Already implemented in current versions