Improve policy/pap csit automation test cases

As a ONAP developer, I would like to improve the csit test cases for policy-pap component and remove all the duplicate lines of code, create standard keywords that can be used for making rest calls and verifying results. Thereby improving the maintainability of the test cases.

Current test cases are here - https://github.com/onap/policy-docker/blob/master/csit/pap/tests/pap-test.robot