Enable IPv6 for MySQL service

ipv6

#1

Currently we have

$ grep -R bind /etc/mysql
/etc/mysql/my.cnf:bind-address		= 127.0.0.1

To enable local ipv6 loopback see https://dev.mysql.com/doc/refman/5.5/en/server-options.html#option_mysqld_bind-address

/etc/mysql/my.cnf:bind-address		= ::

If the address is ::, the server accepts TCP/IP connections on all server host IPv4 and IPv6 interfaces. Use this address to permit both IPv4 and IPv6 connections on all server interfaces.

ps: Applies both for precise and trusty.

Migrated from https://github.com/travis-ci/travis-ci/issues/9861