Allow user to specify URLs on the command line, and use that to allow per-target tokens. (#1901)

Also:
- Parse targets on startup and catch badly formed ones before Scope can start.
- If no port is specified, use default port for scheme; if no scheme is specificed, use 4040.
- Use username as probe token

extras/fixprobe/main.go

@@ -6,6 +6,7 @@ import (
 	"fmt"
 	"io/ioutil"
 	"log"
+	"net/url"
 	"time"
 
 	"github.com/ugorji/go/codec"
@@ -45,11 +46,16 @@ func main() {
 		}
 	}
 
+	url, err := url.Parse(fmt.Sprintf("http://%s", *publish))
+	if err != nil {
+		log.Fatal(err)
+	}
+
 	client, err := appclient.NewAppClient(appclient.ProbeConfig{
 		Token:    *publishToken,
 		ProbeID:  *publishID,
 		Insecure: false,
-	}, *publish, *publish, nil)
+	}, *publish, *url, nil)
 	if err != nil {
 		log.Fatal(err)
 	}