When 'repair' finds a block that is different one the various
parts of the mirror. it is meant to write a chosen good version
to the others.  However it currently writes out the original data
to each. The memcpy to make all the data the same is missing.

Also correct a test so that 'repair' causes a repair, rather than
anything other then 'repair'.
Signed-off-by: Neil Brown <neilb@suse.de>
Signed-off-by: Adrian Bunk <bunk@stusta.de>