TT#36177 Terminate ssh connection during reboot via timeout

This is supposed to fix the hanging SSH connection when
triggering the reboot:

| jenkins@jenkins-slave7:~$ ssh -o ServerAliveInterval=5 -o ServerAliveCountMax=1 -o StrictHostKeyChecking=no -o UserKnownHostsFile=/dev/null -i [...] sudo reboot -f
| [...]
| Rebooting.
| Timeout, server ec2-[...].eu-west-1.compute.amazonaws.com not responding.

Without ServerAliveInterval + ServerAliveCountMax options
the session might get stuck at "Rebooting", timing out only
after 2 hours at worst (which is the TCP keepalive default
timeout, see /proc/sys/net/ipv4/tcp_keepalive_time).

Also drop the force option of reboot, which is causing troubles
on sysv systems. The ssh process isn't terminated cleanly then,
but ssh is running into the TCP keepalive timeout then.
It seems also our systemd backport with the async reboot/halt/poweroff
patch works fine, while with the "-f" option it's failing similar
to the sysv situation.

Change-Id: I3c2c36234d6282f96073ef558fe287d0ac3fa192

ec2-create-ce

@@ -443,7 +443,7 @@ ssh -o "StrictHostKeyChecking=no" -o "UserKnownHostsFile=/dev/null" -i "${KEY_FI
 if $_opt_skip_reboot ; then
   echo "*** Skipping system reboot of instance ID ${INSTANCE_ID} as requested via --skip-reboot ***"
 else
-  ssh -o "StrictHostKeyChecking=no" -o "UserKnownHostsFile=/dev/null" -i "${KEY_FILE}" "admin@$HOSTNAME" "sudo reboot -f"
+  ssh -o "ServerAliveInterval=10" -o "ServerAliveCountMax=1" -o "StrictHostKeyChecking=no" -o "UserKnownHostsFile=/dev/null" -i "${KEY_FILE}" "admin@$HOSTNAME" "sudo reboot"
   retry=120 # up to 10 minutes
   STATUS=""
   while [ "$STATUS" != "running" ] && [ $retry -ne 0 ] ; do