Prozlach/unittests

Unittests for check-zonesync
As you already know i prefer writing shot test functions. Personally i would isolate this function (and other long functions) into new test case.

It would look like this:

```python
class TestHostDataVerification(unittest.TestCase):
  def setUp(self):
    self.host_name = "example-host"
    self.zone = "example.com"
    self.hash = {"ip": "1.2.3.4",
                 "port": 53,
                 "key-id": "example-key",
                 "key-data": "1234567890abcdef",
                 "master": True,
                 }

  def test_verify_host_data_correct(self):
    msg = check_zonesync._verify_host_data(host_hash=self.hash,
                                           zone=self.zone,
                                           host_name=self.host_name)
    self.assertEqual(msg, [])

  def test_verify_host_data_bad_ip(self):
    self.hash["ip"] = "1000.1.2.3.4"
    msg = check_zonesync._verify_host_data(host_hash=self.hash,
                                           zone=self.zone,
                                           host_name=self.host_name)
    self.assertEqual(len(msg), 1)

  def test_verify_host_data_missing_ip(self):
    del self.hash["ip"]
    msg = check_zonesync._verify_host_data(host_hash=self.hash,
                                           zone=self.zone,
                                           host_name=self.host_name)
    self.assertEqual(len(msg), 1)

  def test_verify_host_data_malformed_port(self):
    self.hash["port"] = "53."
    msg = check_zonesync._verify_host_data(host_hash=self.hash,
                                           zone=self.zone,
                                           host_name=self.host_name)
    self.assertEqual(len(msg), 1)

  def test_verify_host_data_incomplete_key_set(self):
    del self.hash["key-data"]
    msg = check_zonesync._verify_host_data(host_hash=self.hash,
                                           zone=self.zone,
                                           host_name=self.host_name)
    self.assertEqual(len(msg), 1)

  def test_verify_host_data_without_keys(self):
    del self.hash["key-id"]
    del self.hash["key-data"]
    msg = check_zonesync._verify_host_data(host_hash=self.hash,
                                           zone=self.zone,
                                           host_name=self.host_name)
    self.assertEqual(msg, [])

  def test_verify_host_data_malformed_key_id(self):
    self.hash["key-id"] = 'this is not a proper key'
    msg = check_zonesync._verify_host_data(host_hash=self.hash,
                                           zone=self.zone,
                                           host_name=self.host_name)
    self.assertEqual(len(msg), 1)

  def test_verify_host_data_malformed_key_data(self):
    self.hash["key-data"] = 'aasfasdfdasf-asdfdas dasf'
    msg = check_zonesync._verify_host_data(host_hash=self.hash,
                                           zone=self.zone,
                                           host_name=self.host_name)
    self.assertEqual(len(msg), 1)
```