Principal: validate type of input parameter

Bytes are unsupported and we should raise a TypeError from Principal
__init__ method otherwise we get hard to debug result

Reviewed-By: Christian Heimes <cheimes@redhat.com>

ipapython/kerberos.py

@@ -66,7 +66,12 @@ class Principal(object):
     Container for the principal name and realm according to RFC 1510
     """
     def __init__(self, components, realm=None):
-        if isinstance(components, six.string_types):
+        if isinstance(components, six.binary_type):
+            raise TypeError(
+                "Cannot create a principal object from bytes: {!r}".format(
+                    components)
+            )
+        elif isinstance(components, six.string_types):
             # parse principal components from realm
             self.components, self.realm = self._parse_from_text(
                 components, realm)