Add safe DirectiveSetter context manager
installutils.set_directive() is both inefficient and potentially
dangerous. It does not ensure that the whole file is written and
properly synced to disk. In worst case it could lead to partially
written or destroyed config files.
The new DirectiveSetter context manager wraps everything under an easy
to use interface.
https://pagure.io/freeipa/issue/7312
Signed-off-by: Christian Heimes <cheimes@redhat.com>
Reviewed-By: Florence Blanc-Renaud <frenaud@redhat.com>