[vcloud_director] network model fence_mode and ip_shared attributes


Updates to the network Model now it is based on get_network_complete:

network.fence_mode returns the FenceMode of the network: 'isolated' or 'natRouted'

network.is_shared returns the IsShared attribute of the network: 'true' or 'false' (as a String).

Arguably is_shared (and also is_inherited) should return a Ruby boolean - happy to update with more code to correct this.