Tests fail for newer versions of Consul

[ShaheedHaque]

The current tests work just fine against (for example) Consul v1.7.4 but fail with newer versions such as v1.9.3 because Consul seems to have added extra output to some of its responses. For example test_agent_services expects a response like this:

            {
                'foo': {'ID': 'foo',
                        'Service': 'foo',
                        'Tags': [],
                        'Meta': {},
                        'Port': 0,
                        'Address': '',
                        'Weights': {'Passing': 1, 'Warning': 1},
                        'EnableTagOverride': False}, 
            }

but v1.9.3 causes the test to fail because of an extra entry Datacenter:

E           {
E            'foo': {'Address': '',
E         +          'Datacenter': 'dc1',
E                    'EnableTagOverride': False,
E                    'ID': 'foo',
E                    'Meta': {},
E                    'Port': 0,
E                    'Service': 'foo',
E                    'Tags': [],
E                    'Weights': {'Passing': 1,
E                                'Warning': 1}},
E           }

I'm happy to provide a PR to address this, but I need some guidance as to how the delta should be addressed. I'd prefer to just upgrade the expected response to match current Consul, but am happy to consider reasonable alternative approaches.