Swap index+n1ql node rebalance failed

Build 6.0.0-1693

Observed that in high data density test with 30 buckets, swap rebalance for index+query node failed with reason "cannot assign requested address"
The setup has 30 buckets and 2 indexes per bucket and ongoing queries on each bucket.
Note that swap rebalance after this failed rebalance is successful. 

Logs-
Index+query node which is rebalanced in- https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-arke-multi-bucket-249/172.23.97.15.zip
Index+query node- https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-arke-multi-bucket-249/172.23.97.19.zip
Index+query node which is rebalanced out- https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-arke-multi-bucket-249/172.23.97.20.zip
KV node- https://s3.amazonaws.com/bugdb/jira/index_reb_multibucket/collectinfo-2019-01-08T151840-ns_1%40172.23.97.12.zip
KV node- https://s3.amazonaws.com/bugdb/jira/index_reb_multibucket/collectinfo-2019-01-08T151840-ns_1%40172.23.97.13.zip
KV node- https://s3.amazonaws.com/bugdb/jira/index_reb_multibucket/collectinfo-2019-01-08T151840-ns_1%40172.23.97.14.zip
FTS node- https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-arke-multi-bucket-249/172.23.96.20.zip
Analytics node- https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-arke-multi-bucket-249/172.23.96.23.zip
Eventing node- https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-arke-multi-bucket-249/172.23.97.177.zip