quorum: Create BDRVQuorumState and BlkDriver and do init. Create the structure holding the quorum settings and write the minimal block driver instanciation boilerplate. Signed-off-by: Benoit Canet <benoit@irqsave.net> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>