[FTS] /api/nsstats becomes unresponsive from time to time

Don't have exact scenario to reproduce it. But I keep noticing this behavior on latest FTS builds from time to time.

error log:
[ns_server:error,2017-06-22T08:32:43.071-07:00,ns_1@172.23.99.211:index_stats_collector-fts<0.1402.0>:index_rest:get_json:42]Request to (fts) http://127.0.0.1:8094/api/nsstats failed: {error,timeout}

All logs:

https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-atlas-3507/172.23.99.211.zip

https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-atlas-3507/172.23.99.39.zip

https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-atlas-3507/172.23.99.40.zip