package mysql-server-5.7 5.7.11-0ubuntu6 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1

[Lucia Fresno]

i used to have issues with phpmyadmin and mysql server/client instalations
but I have no idea why this happened

ProblemType: Package
DistroRelease: Ubuntu 16.04
Package: mysql-server-5.7 5.7.11-0ubuntu6
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: Tue Apr 26 09:08:59 2016
ErrorMessage: subprocess installed post-installation script returned error exit status 1
InstallationDate: Installed on 2016-03-15 (42 days ago)
InstallationMedia: Ubuntu 15.10 "Wily Werewolf" - Release amd64 (20151021)
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
MySQLVarLibDirListing: ['ib_logfile0', 'debian-5.7.flag', 'ibdata1', 'myDB', 'ibtmp1', 'sys', 'ib_logfile1', 'debian-5.6.flag', 'performance_schema', 'mysql', 'mysql_upgrade_info', 'auto.cnf', 'ib_buffer_pool']
ProcCmdline: BOOT_IMAGE=/boot/vmlinuz-4.2.0-35-generic root=UUID=86495013-071b-49cf-a24a-180d01bab869 ro quiet splash vt.handoff=7
RelatedPackageVersions:
 dpkg 1.18.4ubuntu1
 apt 1.2.10ubuntu1
SourcePackage: mysql-5.7
Title: package mysql-server-5.7 5.7.11-0ubuntu6 failed to install/upgrade: subprocess installed post-installation script returned error exit status 1
UpgradeStatus: Upgraded to xenial on 2016-04-26 (0 days ago)