Initial issue was getting the error of 'Normalised Node is already set' 

Further solution is based on the tests created to analyse ODL parser , see the following patches:

• test to confirm that jsonReader is able to iterate over multiple data trees : https://gerrit.onap.org/r/c/cps/+/131357/5/cps-service/src/test/groovy/org/onap/cps/utils/GsonSpec.groovy
• test to parse multiple data tree with json parser: https://gerrit.onap.org/r/c/cps/+/131357/5/cps-service/src/test/groovy/org/onap/cps/utils/JsonParserStreamSpec.groovy