Add pylint guard to import of ipaplatform in ipapython.certdb
ipaplatform is not available in PyPI wheel packages. The guard silences
a pylint error in wheel pylint tests.
https://fedorahosted.org/freeipa/ticket/6474
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Stanislav Laznicka <slaznick@redhat.com>