Install tools for AWS verification

Change-Id: Id4c9c8fe04cba9fd132462a55f926f030fc155e8
diff --git a/Makefile b/Makefile
index 820c581..5129e81 100644
--- a/Makefile
+++ b/Makefile
@@ -33,7 +33,10 @@
         {printf "\033[36m%-30s\033[0m %s\n", $$1, $$2}; \
     '
 
-yang-lint:
+pyang:
+	pyang -v || pip install pyang
+
+yang-lint: pyang
 	#pyang --lint ./config-models/*.x/files/yang/*.yang
 	pyang --lint ./config-models/aether-1.x/files/yang/*.yang
 	pyang --lint ./config-models/aether-2.x/files/yang/*.yang