RadosClient: Enable pool existence check

Pool create interfaces would now refer to updated osdmap
for pool existence, such that an appropriate message is
thrown to the user when run via CLI.

Fixes: #8835
Signed-off-by: Pavan Rallabhandi <pavan.rallabhandi@sandisk.com>
Merge pull request #2209 from somnathr/wip-sd-check-pool-existence

RadosClient: Adding pool existence checks for pool create interfaces.

Reviewed-by: Sage Weil <sage@redhat.com>