Add helper class for core network handling in CI

This adds a helper class to manage various core networks in the CI
testing framework. Specifically, it reads from a YAML file information
such as a node, (un-)deployment script (file), log collection
instructions, etc., in order to allow a common interface to be used to
deploy and undeploy various core network implementations.

This commit adds the class (in cls_corenetwork.py) as well as tests for
this class.

ci-scripts/tests/README.md

@@ -12,6 +12,7 @@ To run individual unit tests, start them like so:
 
     python tests/build.py -v
     python tests/cmd.py -v
+    python tests/corenetwork.py -v
     python tests/deployment.py -v
     python tests/iperf-analysis.py -v
     python tests/ping-iperf.py -v