don't show the grep in build_libvirt.sh

tools/build_libvirt.sh

@@ -406,7 +406,7 @@ if [ "$WAIT_TILL_LAUNCH" = "1" ]; then
       sleep 1
     done
 
-    tail -n +1 -F $VM_DIR/console.log &
+    tail -F $VM_DIR/console.log &
 
     TAIL_PID=$!
 
@@ -418,11 +418,15 @@ if [ "$WAIT_TILL_LAUNCH" = "1" ]; then
     # Let Ctrl-c kill tail and exit
     trap kill_tail SIGINT
 
+    set +o xtrace
+
     echo "Waiting stack.sh to finish..."
     while ! cat $VM_DIR/console.log | grep -q 'All done' ; do
-        sleep 5
+        sleep 1
     done
 
+    set -o xtrace
+
     kill $TAIL_PID
 
     if grep -q "stack.sh failed" $VM_DIR/console.log; then