Merge branch 'develop' into 'master'

nucleus/cli-handling.go

nucleus/clientConfig.go

nucleus/controller.go

nucleus/controller_test.go

nucleus/device.go

nucleus/device_test.go

nucleus/errors.go

nucleus/gnmi_transport.go

nucleus/gnmi_transport_test.go

nucleus/http.go

nucleus/http_test.go

nucleus/initialise_test.go

nucleus/interfaces/client.go

nucleus/interfaces/clientConfig.go

nucleus/nucleus-core.go

nucleus/principalNetworkDomain.go

nucleus/principalNetworkDomain_test.go

nucleus/restconf_transport.go

nucleus/restconf_transport_test.go

nucleus/southbound.go