validate: check the version of python-notario

validate: check the version of python-notario

If the version of python-notario is < 0.0.13 an error message is given
like "TypeError: validate() got an unexpected keyword argument
'defined_keys'", which is not helpful in figuring
out you've got an incorrect version of python-notario.

This check will avoid that situation by telling the user that they need
to upgrade python-notario before they hit that error.

Signed-off-by: Andrew Schoen <aschoen@redhat.com>