package mysql-server-8.0 8.0.17-0ubuntu2 failed to install/upgrade: installed mysql-server-8.0 package post-installation script subprocess returned error exit status 1

[Cygnus]

upgrade from 19.04 to 19.10 errored due to this.

ProblemType: Package
DistroRelease: Ubuntu 19.10
Package: mysql-server-8.0 8.0.17-0ubuntu2
ProcVersionSignature: Ubuntu 5.0.0-36.39-generic 5.0.21
Uname: Linux 5.0.0-36-generic x86_64
ApportVersion: 2.20.11-0ubuntu8.2
Architecture: amd64
Date: Fri Nov 15 14:18:22 2019
ErrorMessage: installed mysql-server-8.0 package post-installation script subprocess returned error exit status 1
InstallationDate: Installed on 2019-05-09 (189 days ago)
InstallationMedia: Ubuntu 19.04 "Disco Dingo" - Release amd64 (20190416)
Logs.var.log.daemon.log:

MySQLConf.etc.mysql.conf.d.mysql.cnf: [mysql]
MySQLConf.etc.mysql.conf.d.mysqldump.cnf:
 [mysqldump]
 quick
 quote-names
 max_allowed_packet = 16M
MySQLConf.etc.mysql.mysql.conf.d.mysqld_safe_syslog.cnf:
 [mysqld_safe]
 syslog
ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-5.0.0-36-generic root=UUID=ed45bdc5-37d7-4b89-92ab-d8f961778f37 ro quiet splash
Python3Details: /usr/bin/python3.7, Python 3.7.5rc1, python3-minimal, 3.7.5-1
PythonDetails: /usr/bin/python2.7, Python 2.7.17rc1, python-minimal, 2.7.17-1
RelatedPackageVersions:
 dpkg 1.19.7ubuntu2
 apt 1.9.4
SourcePackage: mysql-8.0
Title: package mysql-server-8.0 8.0.17-0ubuntu2 failed to install/upgrade: installed mysql-server-8.0 package post-installation script subprocess returned error exit status 1
UpgradeStatus: Upgraded to eoan on 2019-11-15 (0 days ago)

[Robie Basak (racb)]

From log:

2019-11-15T14:50:36.645127Z 0 [ERROR] [MY-000067] [Server] unknown variable 'query_cache_limit=1M'.