This is 10.4 version.
Idea is to create monitor thread for both donor and joiner that will
periodically if needed extend systemd timeout while SST is being
processed. In 10.4 actual SST is executed by running SST script
and exchanging messages on pipe using blocking fgets. This fix
starts monitoring thread before SST script is started and
we stop monitoring thread when SST has been completed.
8a931e4d16