we need to stop server instance on upgrade, but it may be started either by SysV init script or by SystemD.
this commit adds `mysql` target to `systemctl stop` call.
`mysql` may be the name of initscript or an alias while `mariadb` is
a systemd unit file.
RPM solution:
Make all server plugins to restart the server when installed.
To avoid multiple server restarts, do it only once in posttrans scriptlet.
Add support for CPACK_RPM_<component>_POST_TRANS_SCRIPT_FILE
