weldr: Log when starting and finishing metadata preload

It is difficult to tell if these are really running in parallel or not,
even with loggin, but it helps. They will all always start at the same
time (because they are run concurrently with goroutines) and if things
work right should be finished at about the same time.

internal/weldr/api.go

@@ -305,8 +305,10 @@ func (api *API) ServeHTTP(writer http.ResponseWriter, request *http.Request) {
 // This starts a background depsolve for all known distros in order to preload the
 // metadata.
 func (api *API) PreloadMetadata() {
+	log.Printf("Starting metadata preload goroutines")
 	for _, distro := range api.distros {
 		go func(distro string) {
+			startTime := time.Now()
 			d := api.getDistro(distro)
 			if d == nil {
 				log.Printf("GetDistro - unknown distribution: %s", distro)
@@ -324,6 +326,7 @@ func (api *API) PreloadMetadata() {
 			if err != nil {
 				log.Printf("Problem preloading distro metadata for %s: %s", distro, err)
 			}
+			log.Printf("Finished preload of %s in %v", distro, time.Since(startTime))
 		}(distro)
 	}
 }