[xenserver|compute] added create_vlan request
[xenserver|compute] added destroy_vlan request
[xenserver|compute] added create_vlan request tests
[xenserver|compute] added destroy_vlan request tests
[xenserver|compute] added create_network request
[xenserver|compute] added create_network tests
[xenserver|compute] added destroy_network request
[xenserver|compute] added destroy_network request tests
[xenserver|compute] added VLAN model and tests
[xenserver|compute] Added Vlans collection and tests
[xenserver|compute] added save and destroy operations to Network

- Added also required tests
[xenserver|compute] updated compute service to add new model, requests

- added VLAN model
- added Vlans collection
- added create_network request
- added create_vlan req.
- added destroy_network req.
- added destroy_vlan req.
[xenserver|compute] Added Network/VLANs creation example
Merge pull request #1700 from bvox/xenserver-network-additions

Xenserver network additions