[vSphere] Refactor and extend network interface methods (similar to the ovirt implementation)
* added methods to add, remove and update interfaces for vSphere
* added missing method to retrieve the interface
* added existing attribute key to interface (required for modifying, deleting interfaces)
* alias interface's mac to id
Merge pull request #1775 from grimme-atix-de/modify_interface

[vSphere] Refactor and extend network interface methods (similar to the ovirt Implementation)