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

sudo apt-get install mysql-server
Reading package lists... Done
Building dependency tree
Reading state information... Done
mysql-server is already the newest version (5.7.12-0ubuntu1).
0 upgraded, 0 newly installed, 0 to remove and 0 not upgraded.
2 not fully installed or removed.
After this operation, 0 B of additional disk space will be used.
Do you want to continue? [Y/n] y
Setting up mysql-server-5.7 (5.7.12-0ubuntu1) ...
Job for mysql.service failed because the control process exited with error code. See "systemctl status mysql.service" and "journalctl -xe" for details.
invoke-rc.d: initscript mysql, action "start" failed.
dpkg: error processing package mysql-server-5.7 (--configure):
 subprocess installed post-installation script returned error exit status 1
dpkg: dependency problems prevent configuration of mysql-server:
 mysql-server depends on mysql-server-5.7; however:
  Package mysql-server-5.7 is not configured yet.

dpkg: error processing package mysql-server (--configure):
 dependency problems - leaving unconfigured
No apport report written because the error message indicates its a followup error from a previous failure.
                          Errors were encountered while processing:
 mysql-server-5.7
 mysql-server
E: Sub-process /usr/bin/dpkg returned an error code (1)

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lsb_release -rd
Description: Ubuntu 16.04 LTS
Release: 16.04

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I expect to install mysql on ubuntu. I had no error before. Now I get this error, that there was a previous failure. But there was not.

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I would appreciate some help, if possbile. I know that you are all really busy. I guess I could also reinstall Ubuntu, etc. Thank you.

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: mysql-server-5.7 5.7.12-0ubuntu1
ProcVersionSignature: Ubuntu 4.4.0-21.37-generic 4.4.6
Uname: Linux 4.4.0-21-generic x86_64
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
Date: Thu Apr 28 16:02:42 2016
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationDate: Installed on 2016-04-25 (2 days ago)
InstallationMedia: Ubuntu 16.04 LTS "Xenial Xerus" - Release amd64 (20160420.1)
Logs.var.log.daemon.log:

Logs.var.log.mysql.error.log:
 2016-04-28T14:02:36.123612Z 0 [Warning] TIMESTAMP with implicit DEFAULT value is deprecated. Please use --explicit_defaults_for_timestamp server option (see documentation for more details).
 2016-04-28T14:02:38.075610Z 0 [Warning] InnoDB: New log files created, LSN=45790
 2016-04-28T14:02:38.519610Z 0 [Warning] InnoDB: Creating foreign key constraint system tables.
 2016-04-28T14:02:38.707610Z 0 [ERROR] unknown variable 'log=/var/log/mysql-logfile'
 2016-04-28T14:02:38.707610Z 0 [ERROR] Aborting
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
MySQLVarLibDirListing: ['ib_logfile1', 'ib_logfile0', 'debian-5.7.flag', 'ib_buffer_pool', 'ibdata1']
ProcCmdline: BOOT_IMAGE=/vmlinuz-4.4.0-21-generic root=/dev/mapper/ubuntu--vg-root ro acpi=off
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: No upgrade log present (probably fresh install)
modified.conffile..etc.mysql.mysql.cnf: [modified]
mtime.conffile..etc.mysql.mysql.cnf: 2016-04-27T01:14:37.303068