blkverify: Extract qemu_iovec_clone() and qemu_iovec_compare() from blkverify. qemu_iovec_compare() will be used to compare IOs vectors in quorum blkverify mode. The patch extracts these functions in order to factorize the code. Signed-off-by: Benoit Canet <benoit@irqsave.net> Reviewed-by: Max Reitz <mreitz@redhat.com> Signed-off-by: Kevin Wolf <kwolf@redhat.com>