http: Evaluate DB requests in 'non-blocking'.

* src/cuirass/http.scm (handle-builds-request): Wrap 'db-get-builds'
into 'non-blocking'.

src/cuirass/http.scm

@@ -67,8 +67,11 @@
 (define (handle-builds-request db filters)
   "Retrieve all builds matched by FILTERS in DB and convert them to hydra
   format."
-  (let ((builds (with-time-logging "builds request"
-                                   (db-get-builds db filters))))
+  ;; Since these requests can take several seconds (!), run them through
+  ;; 'non-blocking'.
+  (let ((builds (non-blocking
+                 (with-time-logging "builds request"
+                                    (db-get-builds db filters)))))
     (map build->hydra-build builds)))
 
 (define (request-parameters request)