package mysql-server-5.7 5.7.12-0ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

[Witoslaw Koczewski]

got this error while upgrading to 16.04

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: mysql-server-5.7 5.7.12-0ubuntu1
ProcVersionSignature: Ubuntu 4.2.0-35.40-generic 4.2.8-ckt5
Uname: Linux 4.2.0-35-generic x86_64
NonfreeKernelModules: wl
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
Date: Mon Apr 25 19:37:43 2016
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationDate: Installed on 2014-10-16 (556 days ago)
InstallationMedia: Ubuntu 14.04.1 LTS "Trusty Tahr" - Release amd64 (20140722.2)
Logs.var.log.daemon.log:

MySQLConf.etc.mysql.conf.d.mysql.cnf: [mysql]
MySQLConf.etc.mysql.conf.d.mysqld_safe_syslog.cnf:
 [mysqld_safe]
 syslog
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
MySQLVarLibDirListing: ['ib_buffer_pool', 'auto.cnf', 'debian-5.6.flag', 'mysql', 'ib_logfile0', 'debian-5.7.flag', 'debian-5.5.flag', 'ibdata1', 'ib_logfile1', 'performance_schema', 'hu', 'ww', 'mysql_upgrade_info']
ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.2.0-35-generic root=UUID=a0c369c8-282b-4ce7-b9cd-b2435a7e1809 ro splash quiet intel_pstate=disable vt.handoff=7
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1
 apt 1.2.10ubuntu1
SourcePackage: mysql-5.7
Title: package mysql-server-5.7 5.7.12-0ubuntu1 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: Upgraded to xenial on 2016-04-25 (0 days ago)

[Launchpad Janitor (janitor)]

Status changed to 'Confirmed' because the bug affects multiple users.