Tests: fix option name for dsctl
389-ds-base has modified one option name in dsctl, and our test
test_uninstallation.py::TestUninstallBase::()::test_failed_uninstall
is still using the old option (--doit) instead of the new one
(--do-it).
Fixes: https://pagure.io/freeipa/issue/7856
Reviewed-By: Rob Crittenden <rcritten@redhat.com>