BUG-843 : Added description to meter types yang model.

Signed-off-by: Deepthi V V <deepthi.v.v@ericsson.com>
Change-Id: Iedb115fa2178178d79292705f787502df56ab844
Signed-off-by: Moiz Raja <moraja@cisco.com>
BUG-845 Adding FlowRef,GroupRef and MeterRef for the ErrorNotification Message

Signed-off-by: Govind <p.govinda.rajulu@ericsson.com>
Change-Id: I8b851733a4947a6757e14faa6098dafd7b8e7ebb
Signed-off-by: Moiz Raja <moraja@cisco.com>