mysql: Fix of 3 CVEs

CVE-2018-2562: fix DoS / data corruption in partitioned MEMORY tables Server: Partition - CVE-2018-2773: warn when --pid-file is in a world-writable location BUG26585560 - CVE-2018-3174: stop server as the mysql user in mysql.init so an attacker who controls the pid file cannot trick init into...