cbbackupmgr: SQLite compact failing with "cannot VACUUM" error

Found during performance tests of compaction, with SQLite as the storage type. Logs show that we receive the following error on running compact:

2019-06-03T05:15:11.585-07:00 (Cmd) Compacting incr backup `2019-06-03T05_11_01.359023856-07_00` of backup `default` failed: cannot VACUUM from within a transaction

Worth pointing out that this isn't (or at least shouldn't be) an incremental backup. This is just one full backup followed by a compact.

First run

http://perf.jenkins.couchbase.com/job/leto/9990/console

Logs

https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9990/leto-srv-01.perf.couchbase.com.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9990/leto-srv-02.perf.couchbase.com.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9990/leto-srv-03.perf.couchbase.com.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9990/leto-srv-04.perf.couchbase.com.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9990/tools.zip

Second run

http://perf.jenkins.couchbase.com/job/leto/9991/

Logs

https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9991/leto-srv-01.perf.couchbase.com.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9991/leto-srv-02.perf.couchbase.com.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9991/leto-srv-03.perf.couchbase.com.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9991/leto-srv-04.perf.couchbase.com.zip
https://s3-us-west-2.amazonaws.com/perf-artifacts/jenkins-leto-9991/tools.zip