Adding nst.yang and nsi.yang to data model.

Some modifications to nsd-base and instantiation-parameters.
Added new models to Makefile.

Change-Id: I73f77b79876265a07a940e42911d5189e02b2266
Signed-off-by: jdelacruz <jdelacruz@cttc.es>
diff --git a/Makefile b/Makefile
index 9f0d92b..990b4eb 100644
--- a/Makefile
+++ b/Makefile
@@ -21,7 +21,7 @@
 PYBINDPLUGIN:=$(shell /usr/bin/env python3 -c \
 	            'import pyangbind; import os; print("{}/plugin".format(os.path.dirname(pyangbind.__file__)))')
 
-YANG_DESC_MODELS := vnfd nsd
+YANG_DESC_MODELS := vnfd nsd nst nsi
 YANG_RECORD_MODELS := vnfr nsr
 PYTHON_MODELS := $(addsuffix .py, $(YANG_DESC_MODELS))
 YANG_DESC_TREES := $(addsuffix .tree.txt, $(YANG_DESC_MODELS))