x86_64: Fix 079-Phantom hang with QCG enabled

The 079 test creates "sWatcher" thread. In case of unexpected failure
(e.g. Exception thrown) the sWatcher thread remains alive and it
blocks VM shutdown. We mark the sWarcher thread as daemon and
let VM to stop that thread during shutdown cause by unexpected error.

Change-Id: I0cb0b8bbeb15de47b72ddae1a32fcfea3ef8720e
Signed-off-by: Dmitry Petrochenko <dmitry.petrochenko@intel.com>