An instance can be DRBD8, even if all disks are healthy

Therefore, to find out if an instance is diskless, check that
the instance itself has no disks, not that the number of broken
disks is 0.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>
Fix type error

...and eta-reduce map(lambda i: disks[i], range(len(disks)) to
disks.

Signed-off-by: Klaus Aehlig <aehlig@google.com>
Reviewed-by: Helga Velroyen <helgav@google.com>