Remove erroneous check for empty services in _discoverAndVerify
Unbreak TestDiscoveryVerification.

- Test relied on a mock verification function that was never
  called. We now use urlopen mocking for this.
Commenting a non-obvious test
Cleanup of test_consumer.DiscoveryVerification
Don't rediscover after failed verification.

When verifying an id_res response a consumer usually already has
information to verify that against from the previous discovery.
There are three cases where it should try to rediscover it at this
time:

- There were no pre-discovered information
- The pre-discovered claimed_id was the generic
  'http://../identifier_select'
- The pre-discovered claimed_id doesn't match the one being
  verified.

But we shouldn't do discovery after an arbitrary verification
failure. It's just a failure.
Merge test_verifydisco into test_consumer
Unified and simplified discovery verification tests.
Define shared endpoint and messages in DiscoveryVerification.setUp
Test rediscovery with a succesful discover call.
Die, _discoverAndVerify! Die!