Kill xtrabackup spawned processes

* Send KILL signals to all processed spawned by mysqld
* Refactor OCF script to make it more simple and more understandable

Closes-Bug: 1388779

Change-Id: Ie3f6149d3f97f5e8cf3f1f3329b9e335e551b3e6
Signed-off-by: Sergii Golovatiuk <sgolovatiuk@mirantis.com>
Merge "Kill xtrabackup spawned processes"