[PATCH] testbot/Engine: Kill the child before foking a new one for sacrifices.

[Francois Gouget]

VM::Run() now checks that no process is actively using the VM before
starting the new one. Killing the current process makes more sense
anyway and could help ensure it won't interfere with the new one by
sending TestAgent commands.

Signed-off-by: Francois Gouget 
---

tl;dr;
The TestBot Engine attempted a sacrifice but it backfired and killed it 
instead.

More details:
* The Engine started reverting the w1064v1809 VM.
* When that VM transitionned from reverting to sleeping the Engine 
  realized that it really wanted to run a task on another VM on the same 
  host instead.
* Since the host is set up to only run one VM at a time the TestBot 
  decided to power off w1064v1809 right away so it could prepare this 
  other VM.
* But LibvirtTool was still working on w1064v1809, i.e. it was still 
  registered in VM::ChildPid, causing VM::Run() to refuse to start the 
  poweroff process, as per the new check (c0c486a133f1).
* So VM::Run() returned an error, which should not have been a big deal.
  But for some still unknown reason the Engine then died: I checked and 
  the process is not running anymore despite there being no error (perl 
  or otherwise) in the log.

So restarting the Engine should solve the immediate issue, until this 
race happens again (it took ~9 days for this race to happen so we have 
some time to figure it out).

Applying this patch should prevent the issue from reoccurring.

But I will still try to reproduce the issue here so I can figure out why 
the Engine died.

testbot/lib/WineTestBot/Engine/Scheduler.pm | 1 +
 1 file changed, 1 insertion(+)

diff --git a/testbot/lib/WineTestBot/Engine/Scheduler.pm b/testbot/lib/WineTestBot/Engine/Scheduler.pm
index 2131c6833..be1a1fbc8 100644
--- a/testbot/lib/WineTestBot/Engine/Scheduler.pm
+++ b/testbot/lib/WineTestBot/Engine/Scheduler.pm
@@ -776,6 +776,7 @@ sub _SacrificeVM($$$)
   $Host->{$Victim->Status}--;
   $Host->{dirty}++;
   $Victim->RecordStatus($Sched->{records}, $Victim->Status eq "dirty" ? "dirty poweroff" : "dirty sacrifice");
+  $Victim->KillChild();
   $Victim->RunPowerOff();
   return 1;
 }