Fix CDN button visibility

Only show the Red Hat CDN button if the Subscription
module appears to be running. To achieve that, we do
the same thing as with the HMC button - the CDN
button invisible by default. And enable it only if it
looks like the Subscription module is running.

(cherry picked from commit: aca2975)

Resolves: rhbz#1903178

pyanaconda/ui/gui/spokes/installation_source.glade

@@ -633,9 +633,9 @@
                             <child>
                               <object class="GtkRadioButton" id="cdnRadioButton">
                                 <property name="label" translatable="yes" context="GUI|Software Source">Red Hat _CDN</property>
-                                <property name="visible">True</property>
                                 <property name="can_focus">True</property>
                                 <property name="receives_default">False</property>
+                                <property name="no_show_all">True</property>
                                 <property name="margin_left">12</property>
                                 <property name="use_underline">True</property>
                                 <property name="xalign">0</property>

pyanaconda/ui/gui/spokes/installation_source.py

@@ -854,9 +854,9 @@ def _initialize_closest_mirror(self):
     def _initialize(self):
         threadMgr.wait(constants.THREAD_PAYLOAD)
 
-        # If there is no Subscriptiopn DBus module, disable the CDN radio button
+        # If there is the Subscriptiopn DBus module, make the CDN radio button visible
         if is_module_available(SUBSCRIPTION):
-            gtk_call_once(self._cdn_button.set_no_show_all, True)
+            gtk_call_once(self._cdn_button.set_no_show_all, False)
 
         # Get the current source.
         source_proxy = self.payload.get_source_proxy()