worker: don't hard code path to unix domain socket

Introduce a mandatory argument `address`, which is interpreted as a path
to a unix socket when `-unix` is given or a network address otherwise.

Move the default path to the service file.

Add a more useful usage message when passing `-help` or no arguments.

cmd/osbuild-worker/main.go

@@ -8,6 +8,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"os"
 
 	"github.com/osbuild/osbuild-composer/internal/common"
 	"github.com/osbuild/osbuild-composer/internal/jobqueue"
@@ -67,12 +68,26 @@ func handleJob(client *jobqueue.Client) error {
 }
 
 func main() {
-	var address string
+	var unix bool
-	flag.StringVar(&address, "remote", "", "Connect to a remote composer using the specified address")
+	flag.BoolVar(&unix, "unix", false, "Interpret 'address' as a path to a unix domain socket instead of a network address")
+
+	flag.Usage = func() {
+		fmt.Fprintf(flag.CommandLine.Output(), "Usage: %s [-unix] address\n", os.Args[0])
+		flag.PrintDefaults()
+		os.Exit(0)
+	}
+
 	flag.Parse()
 
+	address := flag.Arg(0)
+	if address == "" {
+		flag.Usage()
+	}
+
 	var client *jobqueue.Client
-	if address != "" {
+	if unix {
+		client = jobqueue.NewClientUnix(address)
+	} else {
 		address = fmt.Sprintf("%s:%d", address, RemoteWorkerPort)
 
 		conf, err := createTLSConfig(&connectionConfig{
@@ -85,8 +100,6 @@ func main() {
 		}
 
 		client = jobqueue.NewClient(address, conf)
-	} else {
-		client = jobqueue.NewClientUnix(address)
 	}
 
 	for {

distribution/osbuild-remote-worker@.service

@@ -5,7 +5,7 @@ After=multi-user.target
 [Service]
 Type=simple
 PrivateTmp=true
-ExecStart=/usr/libexec/osbuild-composer/osbuild-worker --remote %i
+ExecStart=/usr/libexec/osbuild-composer/osbuild-worker %i
 CacheDirectory=osbuild-composer
 Restart=on-failure
 RestartSec=10s

distribution/osbuild-worker@.service

@@ -6,7 +6,7 @@ After=multi-user.target osbuild-composer.socket
 [Service]
 Type=simple
 PrivateTmp=true
-ExecStart=/usr/libexec/osbuild-composer/osbuild-worker
+ExecStart=/usr/libexec/osbuild-composer/osbuild-worker -unix /run/osbuild-composer/job.socket
 Restart=on-failure
 RestartSec=10s
 CPUSchedulingPolicy=batch