Increase memory usage and tail latencies

Several latency and memory tests are showing a regression in build 7.1.0-1264

Memory overhead (%), 1 bucket x 20M x 1KB

1263 - http://perf.jenkins.couchbase.com/job/ares/24171/console -  41

1264 - http://perf.jenkins.couchbase.com/job/ares/24172/console - 62

http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=ares_710-1263_access_02cb&snapshot=ares_710-1264_access_2222

99th Percentile READ Latency(ms), Workload CA, 3 nodes, 12 vCPU, 60K ops/sec, uniform distribution, s=1 c=1000

1260 - http://perf.jenkins.couchbase.com/job/hercules/12719/console - 0.114

1265 - http://perf.jenkins.couchbase.com/job/hercules/12720/console - 0.505

99.9th percentile SET latency (ms), 4 nodes, 1 bucket x 20M x 1KB, 0/100 R/W, 1 thread, 20 ops/sec, Durability Majority

1263 - http://perf.jenkins.couchbase.com/job/ares/24174/console - 2.87

1264 - http://perf.jenkins.couchbase.com/job/ares/24173/console - 3.81

Logs at the bottom of the jobs

http://changelog.build.couchbase.com/?product=couchbase-server&fromVersion=7.1.0&fromBuild=1263&toVersion=7.1.0&toBuild=1264&f_asterixdb=off&f_backup=off&f_cbas-core=off&f_forestdb=off&f_kv_engine=on&f_product-metadata=off