NetConf SBP uses global privatekey for all connections

Problem:
Current implementation of NetConf south bound plugin uses single instance of kaypair for all connected netconf devices. User is able to set username/password per netconf device, but connection key is shared for all connections.

Solution:
When new netconf device configuration is created via in data store in netconf topology, this configuration must contain the username/password or keypair for the device.

What needs to be done:

• netconf model (device configuration) must be adapted in order to contain username/password or keypair in base64 format
• org.opendaylight.netconf.topology.AbstractNetconfTopology
• privateKeyPath and privateKeyPassphrase must be removed (also from blueprint and configuration)
• method getClientConfig must be adapted accordingly