- Added Specific exceptions
- str() instead of concatenation
- removed zone not found warning

Transip sdk also supports a private_key_file,
so forwarding that option to the provider.
Could be handy in combination with k8s secrets.

Fixes an exception in combination
with the yamlProvider as a target
The unmodified value object isn't
represented as string while
building the yaml output
The Exception:
  yaml.representer.RepresenterError:
  ('cannot represent an object', 1.1.1.1)

yaml/representer.py@249,
represent_undefined()

TransIP allows '@' as value to alias the root record.
'@' was on populate appended with the zone, which trigger an unneeded update.
'@' => '@.example.com.' -> 'example.com'
This fix will stop the unneeded update