Multiple initial build index time regressed

Multiple inital build index regressed in 7.2.1-5866

Change logs

http://changelog.build.couchbase.com/?product=couchbase-server&fromVersion=7.2.1&fromBuild=5865&toVersion=7.2.1&toBuild=5866&f_indexing=on 

Initial index (min), 1 bucket x 80M x 1KB, 100K KV ops/sec, single 2i index, large key 1024 char, no mutations during initial build only, PLASMA

Initial index (min), 1 bucket x 500M, single 2i index, 100K KV ops/sec, no mutations during initial build only, PLASMA

logs : 7.2.1-5867

https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-secondary-plasma-8301/172.23.97.10.zip

cbmonitor: http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=nyx_721-5866_build_secondaryindex_4e4f&snapshot=nyx_721-5865_build_secondaryindex_8e9b 

Run: http://perf.jenkins.couchbase.com/job/secondary-plasma/8301/