runtime-install: specify polkit-gnome to avoid lxpolkit and GTK2

blivet-gui-runtime requires PolicyKit-authentication-agent. If
we just let dnf pick what to satisfy that requirement with, it
picks lxpolkit, which requires gtk2. Specifying polkit-gnome
instead should I think give us a smaller footprint, its deps
seem quite small.

Signed-off-by: Adam Williamson <awilliam@redhat.com>

share/templates.d/99-generic/runtime-install.tmpl

@@ -115,6 +115,10 @@ installpkg libblockdev-lvm-dbus
 installpkg volume_key
 installpkg nss-tools
 
+## blivet-gui-runtime requires PolicyKit-authentication-agent, if we
+## don't tell dnf what to pick it picks lxpolkit, which drags in gtk2
+installpkg polkit-gnome
+
 ## enable swap on zram
 installpkg zram-generator-defaults