Do not unconditionally hide nm-appet in Fedora >= 20 (#774)

This is first step of #774 - when NetworkManager enabled, show nm-applet
icon. Still NetworkManager need some configuration to not break ProxyVM
eth0.

rpm_spec/core-vm.spec

@@ -149,7 +149,11 @@ for F in gpk-update-icon nm-applet ; do
 done
 
 echo 'OnlyShowIn=GNOME;UpdateableVM;' >> /etc/xdg/autostart/gpk-update-icon.desktop || :
+if %{fedora} >= 20
+echo 'OnlyShowIn=GNOME;QUBES;' >> /etc/xdg/autostart/nm-applet.desktop || :
+%else
 echo 'OnlyShowIn=GNOME;NetVM;' >> /etc/xdg/autostart/nm-applet.desktop || :
+%endif
 
 usermod -p '' root
 usermod -L user