util: Fix error return for virProcessKillPainfullyDelay()

util: Fix error return for virProcessKillPainfullyDelay()

Commit 93af79fb removed a cleanup label in favor of returning error
values directly in certain cases. But the final return value was changed
from -1 to 0. If we get to the end of the function, that means that
we've waited for the process to exit but it still exists. So we should
return -1. The error message was still being set correctly, but we were
returning a success status (0).

Signed-off-by: Jonathon Jongsma <jjongsma@redhat.com>
Reviewed-by: Ján Tomko <jtomko@redhat.com>