use local yangmodels/openconfig (if present) instead of github

docker/test/getyang.sh

@@ -0,0 +1,19 @@
+#!/usr/bin/env bash
+# Script to get yangmodels, either from local installation, or from remote
+# This is an optimization from always getting it from github inside the dockerfile
+if [ -d yang ]; then
+    rm -rf yang
+fi
+mkdir -p yang/standard
+if [ -d /usr/local/share/yang/standard ]; then
+    cp -R /usr/local/share/yang/standard yang/    
+else
+   cd yang
+   git init
+   git remote add -f origin https://github.com/YangModels/yang
+   git config core.sparseCheckout true
+   echo "standard/" >> .git/info/sparse-checkout
+   echo "experimental/" >> .git/info/sparse-checkout
+   git pull origin main
+fi
+