Don't install novnc from package by default

By default the installation is failed because the novnc package has got
the a dependency of the nova-common package. The last package provides
"/etc/nova/*" files with appropriate privileges. It potentially brings
to the problem of an access to those files.

Change-Id: I1689bef817365b10bf972dc4a8033892ad5939d1
Related-Bug: 1248923
diff --git a/lib/nova b/lib/nova
index b9fa3e1..5b6f50e 100644
--- a/lib/nova
+++ b/lib/nova
@@ -589,7 +589,7 @@
 
     if is_service_enabled n-novnc; then
         # a websockets/html5 or flash powered VNC console for vm instances
-        NOVNC_FROM_PACKAGE=`trueorfalse True $NOVNC_FROM_PACKAGE`
+        NOVNC_FROM_PACKAGE=`trueorfalse False $NOVNC_FROM_PACKAGE`
         if [ "$NOVNC_FROM_PACKAGE" = "True" ]; then
             NOVNC_WEB_DIR=/usr/share/novnc
             install_package novnc