qa: fix rbd cli tests checking size

b43bc1a0b0692818d789f9f489b9aba5dd40522f changed the kilo prefix
from K to k in a few places.

Signed-off-by: Josh Durgin <josh.durgin@inktank.com>
Merge pull request #686 from ceph/wip-rbd-cli-tests

qa: fix rbd cli tests checking size

Reviewed-by: Sage Weil <sage@inktank.com>