services: host-name: Use the host name as the running value.

Previously, the “running value” of the ‘host-name’ service would
be #<unspecified>.  This change makes it more pleasing to the eye.

* gnu/services/base.scm (host-name-service-type): ‘start’ returns NAME.

Change-Id: I38b8320e43639b6623475871ca6fbad3a459eb59

gnu/services/base.scm

@@ -801,7 +801,8 @@ host names."
       (documentation "Initialize the machine's host name.")
       (provision '(host-name))
       (start #~(lambda _
-                 (sethostname #$name)))
+                 (sethostname #$name)
+                 #$name))
       (one-shot? #t)))
    (description "Initialize the machine's host name.")))