qemu wasn't restoring the terminal if it was terminated early

You would need to run reset to regain control of your terminal after
this happened, so this turns off the monitor and serial port mux to
stdout.

Resolves: rhbz#1691632

src/pylorax/installer.py

@@ -214,7 +214,7 @@ class QEMUInstall(object):
         else:
             display_args = opts.vnc
         log.info("qemu %s", display_args)
-        qemu_cmd += ["-nographic", "-display", display_args ]
+        qemu_cmd += ["-nographic", "-monitor", "none", "-serial", "null", "-display", display_args ]
 
         # Setup virtio networking
         qemu_cmd += ["-netdev", "user,id=n1", "-device", "virtio-net-pci,netdev=n1"]