Display runners registration token in CI runners config

app/views/ci/admin/runners/index.html.haml

 %p.lead
-  %span To register a new runner you should enter the following registration token. With this token the runner will request a unique runner token and use that for future communication.
-  %code #{GitlabCi::REGISTRATION_TOKEN}
+  %span
+    To register a new runner you should enter the following registration token.
+    With this token the runner will request a unique runner token and use that for future communication.
+    Registration token is
+    %code #{current_application_settings.runners_registration_token}
 
 .bs-callout
   %p