Multi-key write commands assume all segments have CH.getNumOwners() owners

When handling multi-key write commands, both TriangleDistributionInterceptor and NonTxDistributionInterceptor assume that there are no backup owners when consistentHash.getNumOwners() == 1. But during rebalance some segments can have more than getNumOwners() owners, as the write CH is a union of the current and future CHs, while getNumOwners() always returns the value in the cache configuration.