client: Use http.Client instead of a string for the socket

This converts the client and weldrcheck functions to use http.Client for
connections instead of passing around the socket path and opening it for
each test.

cmd/osbuild-weldr-tests/main.go

@@ -3,9 +3,24 @@
 package main
 
 import (
+	"context"
+	"net"
+	"net/http"
+	"time"
+
 	"github.com/osbuild/osbuild-composer/internal/weldrcheck"
 )
 
 func main() {
-	weldrcheck.Run("/run/weldr/api.socket")
+	client := &http.Client{
+		// TODO This may be too short/simple for downloading images
+		Timeout: 60 * time.Second,
+		Transport: &http.Transport{
+			DialContext: func(_ context.Context, _, _ string) (net.Conn, error) {
+				return net.Dial("unix", "/run/weldr/api.socket")
+			},
+		},
+	}
+
+	weldrcheck.Run(client)
 }