Fix Bug 2091: NS Update on NS Instances fail with database exception on screen...

Fix Bug 2091: NS Update on NS Instances fail with database exception on screen when VNFD ID is incorrect

	- Changed the VNFD ID text field to dropdown field with VNFD Name listed
	- Changed the NSUpdate popup message

Change-Id: Iacf6572eb7e56cfd97a8e871d4671f56c6eb94ba
Signed-off-by: SANDHYA.JS <sandhya.j@tataelxsi.co.in>