spawning netconf connections - missing input validation

Problem:
Following NetConf user guide https://wiki.opendaylight.org/view/OpenDaylight_Controller:Config:Examples:Netconf in new device configuration is added by simply writing device configuration data into network topology model. This approach is very naive, because no validation is done and client gets always 201 (created) response regardless of the fact his configuration was valid or not.
The problem is that direct write into topology model is used instead of RPC call.
In case NETCONF-476 will be fixed, base64 binary data must be part of device configuration which will be difficult to verify on model level.

Solution:
instead of direct write into netconf topology model, new set of RCPs will be created for create/delete netconf device configurations.
existing topology model
netconf/sal-netconf-connector/src/main/yang/netconf-node-topology.yang
must be adapted.
new RPCs: create-device, delete-device will be introduced in user manuals. This solution backwards compatible, because direct writes into netconf topology model are still possible.
create-device, delete-device will verify configuration data before using them and will report error / success to the client application accordingly.