This submission adds method to
rally/benchmark/scenarios/designate/basic.py
1)def list_servers
Added configuration files for server operations under
samples/tasks/scenarios/designate
1) list-servers.json
2) list-servers.yaml
Also, added unittests to test_basic.py under
tests/unit/benchmark/scenarios/designate
Change-Id: I948f5e0c8beca963a9d6f1d388ea0410f2d107e3