installer: Factorize url-alive? in internet check.

* gnu/installer/newt/network.scm (wait-service-online): Factorize url-alive?
in internet check.

gnu/installer/newt/network.scm

@@ -115,6 +115,11 @@ network devices were found. Do you want to continue anyway?"))
 (define (wait-service-online)
   "Display a newt scale until connman detects an Internet access. Do
 FULL-VALUE tentatives, spaced by 1 second."
+  (define (url-alive? url)
+    (false-if-exception
+     (= (response-code (http-request url))
+        200)))
+
   (define (ci-available?)
     (dynamic-wind
       (lambda ()
@@ -122,15 +127,8 @@ FULL-VALUE tentatives, spaced by 1 second."
           (lambda _ #f))
         (alarm 3))
       (lambda ()
-        (or
-          (false-if-exception
-            (= (response-code
-                 (http-request "https://ci.guix.gnu.org"))
-               200))
-          (false-if-exception
-            (= (response-code
-                 (http-request "https://bordeaux.guix.gnu.org"))
-               200))))
+        (or (url-alive? "https://ci.guix.gnu.org")
+            (url-alive? "https://bordeaux.guix.gnu.org")))
       (lambda ()
         (alarm 0))))