Fix minor bug in test_get_root_discovers_v1
Fix minor bug in test_get_root_discovers_v1

Invoke json method to get response body instead of referring it.

Change-Id: I5af060b75b14f2b9322099d8a658c070b056cee2

gilbertpilz/solum,ed-/solum,ed-/solum,devdattakulkarni/test-solum,julienvey/solum,gilbertpilz/solum,gilbertpilz/solum,ed-/solum,stackforge/solum,ed-/solum,stackforge/solum,openstack/solum,openstack/solum,julienvey/solum,gilbertpilz/solum,devdattakulkarni/test-solum