Tackerclient failed to handle yaml load error.

While onboarding a vnfd with infected vnfd file, yaml.load raised exception. But tacker client failed to handle it, and raised traces.

ubuntu@openstack-nti-4:~$ openstack vnf descriptor create --vnfd-file ~/test_vnfd.yaml vnfd1
Traceback (most recent call last):
  File "/usr/lib/python2.7/logging/__init__.py", line 861, in emit
    msg = self.format(record)
  File "/usr/lib/python2.7/logging/__init__.py", line 734, in format
    return fmt.format(record)
  File "/usr/lib/python2.7/logging/__init__.py", line 465, in format
    record.message = record.getMessage()
  File "/usr/lib/python2.7/logging/__init__.py", line 325, in getMessage
    msg = str(self.msg)
TypeError: __str__ returned non-string (type ScannerError)
Logged from file app.py, line 407