FIX: Tests: raid0->raid10 without degradation

FIX: Tests: raid0->raid10 without degradation

raid0->raid10 transition needs at least 2 spare devices.
After level changing to raid10 recovery is triggered on
failed (missing) disks. At the end of recovery process
we have fully operational (not degraded) raid10 array.

Initialy there was possibility to migrate raid0->raid10
without recovery triggering (it results degraded raid10).
Now it is not possible.
This patch adapt tests to new mdadm's behavior.

Signed-off-by: Krzysztof Wojcik <krzysztof.wojcik@intel.com>
Signed-off-by: NeilBrown <neilb@suse.de>