Because reproducibility is extremely important, emubd always zeros
blocks on the first erase, even when erase_value=-1.
Well, at least it should be. We were correctly zeroing the blocks in
RAM, but if erase_value=-1 we were leaving the disk unzeroed, causing
the disk to fall out of sync.
Fixed by zeroing disk in lfs_emubd_createcfg, even if erase_value=-1.
Also I went ahead and dropped the bd->disk->scratch block. We're already
allocating RAM-backed blocks on erase anyways, so keeping scratch around
doesn't really gain us anything anymore. Now there is just a temporary
allocation in lfs_emubd_createcfg to zero the disk efficiently during
initialization.
Christopher Haster
5fbf073bfb