quorum: Add the rewrite-corrupted parameter to quorum

On read operations when this parameter is set and some replicas are corrupted
while quorum can be reached quorum will proceed to rewrite the correct version
of the data to fix the corrupted replicas.

This will shine with SSD where the FTL will remap the same block at another
place on rewrite.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
block: Add node-name argument to drive-mirror

This new argument can be used to specify the node-name of the new mirrored BDS.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
block: Add replaces argument to drive-mirror

drive-mirror will bdrv_swap the new BDS named node-name with the one
pointed by replaces when the mirroring is finished.

Signed-off-by: Benoit Canet <benoit@irqsave.net>
qemu-iotests: Add TestRepairQuorum to 041 to test drive-mirror node-name mode.

The to-replace-node-name is designed to allow repairing of broken Quorum file.
This patch introduce a new class TestRepairQuorum testing that the feature
works.
Some further work will be done on QEMU to improve the robutness of the tests.

Signed-off-by: Benoit Canet <benoit@irqsave.net>