Validate key in otptoken-add

Verify that key is not empty when adding otp token. If it is empty, raise an
appropriate error.

https://fedorahosted.org/freeipa/ticket/6200

Reviewed-By: Martin Basti <mbasti@redhat.com>

ipaserver/plugins/otptoken.py

@@ -323,6 +323,10 @@ class otptoken_add(LDAPCreate):
             except (NotFound, IndexError):
                 pass
 
+        # Check if key is not empty
+        if entry_attrs['ipatokenotpkey'] is None:
+            raise ValidationError(name='key', error=_(u'cannot be empty'))
+
         # Build the URI parameters
         args = {}
         args['issuer'] = issuer