Mysql/InnoDB says it doesn't have access rights to create temp tables, but it does
Found a solution:

Apparently we needed to use k to give lock file permission. So now usr.sbin.mysqld looks like this:

  /var/mysql_tmpfs/ r,
  /var/mysql_tmpfs/** rwk,


We found the answer on the oracle blog: https://blogs.oracle.com/jsmyth/entry/apparmor_and_mysql