BVTCK-36 Deleting UnknownProviderBootstrapTest, because assertions are already covered in other tests

Adding tests for ValidationException being thrown for not loadable validation provider using byProvider and byDefaultProvider for bootstrapping
BVTCK-32 Aligning with latest BV API updates (moving @ConvertGroup into a sub package). Re-enabling tests which failed on RI, but now work due to latest HV fixes.