Cache.lock(key) should throw AvailabilityException in degraded mode

We need a test for cache.lock(key) when one of the owners is not an actual member of the cluster and the cache is in degraded mode. PartitionHandlingInterceptor doesn't handle LockControlCommand explicitly, so it might end up throwing TimeoutException after waiting for a new topology. We should make sure it throws an AvailabilityException instead.