High run-to-run variations in analytics drop tests

We see high run-to-run variations in analytics drop tests. The build used is 7.1.0-1250. After the runs dropped a collection, it took different time to drop the index. 

Avg. drop rate (items/sec), 4 nodes, BigFUN 20M users (320M docs), 3 indexes, SSD, s=1 c=3

http://showfast.sc.couchbase.com/#/runs/bigfun_20M_drop_4n_1s_3c_oceanus/7.1.0-1250

http://perf.jenkins.couchbase.com/job/oceanus/7317/

2021-11-02T15:07:24 [INFO] Dropping collection bucket-1:scope-1.ChirpMessages-1

2021-11-02T15:07:37 [INFO] Number of items in dataset ChirpMessages-1: 200002740

2021-11-02T15:07:50 [INFO] Number of items in dataset ChirpMessages-1: 49996749

2021-11-02T15:08:02 [INFO] Number of items in dataset ChirpMessages-1: 49996749

2021-11-02T15:08:05 [INFO] Number of items in dataset ChirpMessages-1: 0

http://perf.jenkins.couchbase.com/job/oceanus/6886/

2021-09-09T12:38:38 [INFO] Dropping collection bucket-1:scope-1.ChirpMessages-1

2021-09-09T12:38:51 [INFO] Number of items in dataset ChirpMessages-1: 200002740

2021-09-09T12:38:53 [INFO] Number of items in dataset ChirpMessages-1: 0