[CBM] ~60% decrease in restore throughput with TLS enabled

We recently started doing cbbackupmgr restore tests with TLS enabled. We are seeing a large throughput regression when enabling TLS in 7.1.0-2123:

http://perf.jenkins.couchbase.com/job/leto/22848/console No TLS, 340 MB/sec

http://perf.jenkins.couchbase.com/job/leto/22831/console TLS, 146 MB/sec

Cbmonitor comparison:

http://cbmonitor.sc.couchbase.com/reports/html/?snapshot=leto_710-2123_restore_a39b&label=noTLS&snapshot=leto_710-2123_restore_326b&label=TLS

An initial look back at when we added these performance tests reveals that this regression was present with CB 7.1.0-1650 but wasn't noticed (my apologies for that):

http://perf.jenkins.couchbase.com/job/leto/21783/console