table_cache setting is now table_open_cache MySQL 5.6+

[nickhammond]

Installing on a new node and it's installing 5.6 and the template in this role for my.cnf has table_cache which is no longer supported and prevents mysqld from starting up. It's now table_open_cache for >= 5.6.

MySQL ticket: http://bugs.mysql.com/bug.php?id=68315

Since the standard my.cnf file from apt includes all files in /etc/mysql/conf.d/*, why don't we move the settings from my.cnf in the template file into an override that goes in /etc/mysql/conf.d/? Then do a version comparison or conditional include based on the mysql version and add mysql_version as a setting with the role.

Truncated output from running sudo mysqld --verbose:

...
[ERROR] mysqld: unknown variable 'table_cache=64'
[ERROR] Aborting