Minor UI issue: trying to click create new bucket during a rebalance doesn't give the user any reason why it won't work

Setup a cluster, do a rebalance, during the rebalance try to click "create new bucket". It will spin for a second, and then come back to the same screen without indication of why I can't create a new bucket. Would be good to have a small error pop-up saying that you can't create a bucket during a rebalance (which is expected)