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

[BCB]

Before the mysql-server failure this process hung and had to be killed:

root 23810 23781 0 00:52 pts/2 00:00:00 whiptail --backtitle Package configuration --title Configuring lxd --output-fd 11 --nocancel --msgbox lxcbr0 is being replaced by lxdbr0 With this package upgrade LXD is moving away from the LXC provided lxcbr0 bridge and moving to its own lxdbr0 bridge. The reason for this switch is: - Drop the dependency on the old LXC (lxc1) package. - Only run the bridge when LXD is running. - Don't hardcode a subnet which may be used by the user. Important differences between lxcbr0 and lxdbr0: - The lxdbr0 bridge DOES NOT come with ANY configured IPv4 or IPv6 subnet. - The bridge provides basic HTTP connectivity out of the box by way of a tiny HTTP PROXY server running on an IPv6 link-local address. - The user IS EXPECTED to configure the bridge to use an UNUSED subnet on their network. To configure lxdbr0 to your liking, please run: dpkg-reconfigure -p medium lxd To stay on the old lxcbr0 bridge, make sure you have the "lxc1" package installed, then select the "use an existing bridge" option. --scrolltext 20 77

Description: Ubuntu 16.04 LTS
Release: 16.04

mysql-server-5.7:
  Installed: 5.7.11-0ubuntu6
  Candidate: 5.7.11-0ubuntu6
  Version table:
 *** 5.7.11-0ubuntu6 500
        500 http://us-east-1.ec2.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

whiptail:
  Installed: 0.52.18-1ubuntu2
  Candidate: 0.52.18-1ubuntu2
  Version table:
 *** 0.52.18-1ubuntu2 500
        500 http://us-east-1.ec2.archive.ubuntu.com/ubuntu xenial/main amd64 Packages
        100 /var/lib/dpkg/status

I expected the release to be upgraded but one process hung and had to be killed and mysql-server-5.7 failed and let me with an unstable system.

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
ApportVersion: 2.20.1-0ubuntu2
Architecture: amd64
Date: Mon Apr 25 01:26:18 2016
Ec2AMI: ami-c9b8e9ac
Ec2AMIManifest: (unknown)
Ec2AvailabilityZone: us-east-1d
Ec2InstanceType: c3.large
Ec2Kernel: aki-919dcaf8
Ec2Ramdisk: unavailable
ErrorMessage: subprocess installed post-installation script returned error exit status 1
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: ['debian-5.6.flag', 'mysql_upgrade_info', 'mysql', 'debian-5.5.flag', 'ibdata1', 'auto.cnf', 'vtcdata_adb', 'performance_schema', 'debian-5.7.flag', 'ib_logfile1', 'ib_logfile0', 'ib_buffer_pool']
ProcCmdline: root=LABEL=cloudimg-rootfs ro console=hvc0
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 2016-04-25 (0 days ago)
modified.conffile..etc.mysql.mysql.conf.d.mysqld.cnf: [modified]
mtime.conffile..etc.mysql.mysql.conf.d.mysqld.cnf: 2015-08-03T23:01:11.798922