qa/workunit/rbd/copy.sh: do not delete/recreate rbd pool

Among other things, it breaks when tiering is enabled.

Signed-off-by: Sage Weil <sage@inktank.com>
qa/workunit/rbd/import_export.sh: skip list-objects tests with tiering

Listing objects isn't reliable with cache pools; skip that part of the
test if we see that rbd has tiering enabled.

Signed-off-by: Sage Weil <sage@inktank.com>
Merge pull request #1707 from ceph/wip-rbd-test

rbd: fix tests for cache pools

Reviewed-by: Josh Durgin <josh.durgin@inktank.com>