RadosClient: Adding pool existence checks for pool create interfaces.

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.

Objecter: Removing the check in objecter now.

Fixes: #8835
Signed-off-by: Pavan Rallabhandi <pavan.rallabhandi@sandisk.com>
Yes, just a wait_for_osdmap() suffices. But I thought of making the pool create interfaces consistent with others in RadosClient, by having the EEXIST check via osdmap.lookup_pg_pool_name() in RadosClient (and also may avoid a call to Objecter). I could not find any other users of Objecter::create_pool() and thought this to be safe. Please let me know if I am missing anything obvious, would be happy to leave the EEXIST in Objecter.