NETCONF southbound requires notifications.yang model to be present on the device

NETCONF southbound requires notifications.yang model to be present on the device

There is no standardized YANG model for NETCONF notifications simply
because RFC5277 predates YANG and has not been updated. The presence
of the notification capability is enough for notifications to work –
the SchemaContext assembly code supplies the model internally based
on the capability.

JIRA: NETCONF-338
Signed-off-by: vladyslav.marchenko <Vladyslav.Marchenko@pantheon.tech>
Signed-off-by: Jamo Luhrsen <jluhrsen@gmail.com>
Change-Id: Iaec5eab02f8d43f752d90a3fd0ecbc0a57e9e75f