try to use the fqdn for pulpcore urls

Those URLs are used by Katello and clients to connect to Pulp and
`localhost` is almost never the right choice here as it will be either
not reachable (for clients) or have the wrong certs (for Katello).

Try to obtain the FQDN of the system from Facter, if available and fall
back to `Socket.gethostname` (which is not guaranteed to return a FQDN)
otherwise.

lib/smart_proxy_pulp_plugin/pulpcore_plugin.rb

@@ -4,12 +4,20 @@
 
 module PulpProxy
   class PulpcorePlugin < ::Proxy::Plugin
+    fqdn = begin
+      require 'facter'
+      Facter.fact('networking.fqdn').value
+    rescue StandardError, LoadError
+      require 'socket'
+      Socket.gethostname
+    end
+
     plugin "pulpcore", ::PulpProxy::VERSION
-    default_settings :pulp_url => 'https://localhost',
-                     :content_app_url => 'https://localhost:24816/',
+    default_settings :pulp_url => "https://#{fqdn}",
+                     :content_app_url => "https://#{fqdn}/pulp/content/",
                      :mirror => false,
                      :client_authentication => ['password', 'client_certificate'],
-                     :rhsm_url => 'https://localhost/rhsm'
+                     :rhsm_url => "https://#{fqdn}/rhsm"
 
     AUTH_TYPES = ['password', 'client_certificate'].freeze