'Allow sentry: prefixed keys without any registration'

def test_legacy_key(self):

    assert (self.manager.get('sentry:foo') == '')
    self.manager.set('sentry:foo', 'bar')
    assert (self.manager.get('sentry:foo') == 'bar')
    assert self.manager.delete('sentry:foo')
    assert (self.manager.get('sentry:foo') == '')
