drbd: Forcing primary should also work for Consistent disks [Bugz 266]

Up to now this only worked for Outdated and Inconsistent disks, that
it did not worked for Consistent disks was an inconsistent omission.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>