TRUNK-4315: Validates newly created Providers

https://issues.openmrs.org/browse/TRUNK-4315

Users were able to create Providers by specifying both Provider Name and Person,
this violated the rule which required them to only supply one of the two.
The earlier implementation asserted that no errors existed, but the Provider was setup such that both person and provider name were set. So I changed it to look for existence of errors which is the expected behavior. Maybe I can change the method name to shouldFailIfBothPersonAndNameSet() but it does the same thing.