buildbot may leave stale mysqld

There was an attempt to fix this in MDEV-7448, but it didn't work.

When bb slave looses connection to master it seem to send SIGKILL to process group:

2015-03-02 19:03:15-0500 [Broker,client] lost remote

2015-03-02 19:03:15-0500 [Broker,client] lost remote step

2015-03-02 19:03:15-0500 [Broker,client] stopCommand: halting current command <buildslave.commands.shell.SlaveShellCommand instance at 0x10004609998>

2015-03-02 19:03:15-0500 [Broker,client] command interrupted, attempting to kill

2015-03-02 19:03:15-0500 [Broker,client] trying to kill process group 17399

2015-03-02 19:03:15-0500 [Broker,client]  signal 9 sent successfully

2015-03-02 19:03:15-0500 [Broker,client] Lost connection to buildbot.askmonty.org:9989

mysqld is most probably detached from that process group. At least mysql-test/lib/My/SafeProcess/safe_process.cc calls setpgid(). As a result signal won't reach mysqld.

This means that intermediate processes must catch SIGKILL and forward it to mysqld. But SIGKILL cannot be caught.

I can think of 3 ways of fixing this problem:

• let bb use different signal when killing process group (SIGINT, SIGHUP)
• don't detach mysqld from bb process group
• somehow let bb record and kill mysqld process