ipatests: Add compatibility against python-cryptography 3.0
The recently released python-cryptography 3.0 has backward incompatible
changes. One of them [0] breaks FreeIPA self-tests.
Note: this requires python-cryptography 2.7+.
[0] https://github.com/pyca/cryptography/commit/3b2102af549c1095d5478bb1243ee4cf76b9762b
Fixes: https://pagure.io/freeipa/issue/8428
Signed-off-by: Stanislav Levin <slev@altlinux.org>
Reviewed-By: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Rob Crittenden <rcritten@redhat.com>
Reviewed-By: Alexander Bokovoy <abokovoy@redhat.com>