fix the crash seen on get request with random distribution

indexes is applicable only with DIST_KETAMA (gets initialized in DIST_KETAMA switch case) and the logic to choose the server from the cluster indexes should be performed only when the pool->dist_type is set to DIST_KETAMA.
Merge pull request #1 from mshunmugam/multiple_servers_per_node_hash

fixed the crash seen on get request with distribution:random