Add missing R: dconf to hide nm-applet when not used

Without dconf, gsettings uses "memory" backend which isn't saved
anywhere and isn't shared across applications. This makes gsettings
pretty useless.

Fixes QubesOS/qubes-issues#1299

rpm_spec/core-vm.spec

@@ -61,6 +61,8 @@ Requires:   ImageMagick
 Requires:   librsvg2-tools
 Requires:   fakeroot
 Requires:   desktop-notification-daemon
+# to show/hide nm-applet
+Requires:   dconf
 Requires:   pygtk2
 Requires:   zenity
 Requires:   qubes-libvchan