Switch to kingpin flags (#639)

* Switch to kingpin flags

* Fix logrus vendoring

* Fix flags in main tests

* Fix vendoring versions

collector/textfile_test.go

@@ -14,13 +14,14 @@
 package collector
 
 import (
-	"flag"
 	"io/ioutil"
 	"sort"
 	"strings"
 	"testing"
 
 	"github.com/golang/protobuf/proto"
+	"github.com/prometheus/common/log"
+	"gopkg.in/alecthomas/kingpin.v2"
 )
 
 func TestParseTextFiles(t *testing.T) {
@@ -49,7 +50,8 @@ func TestParseTextFiles(t *testing.T) {
 
 		// Suppress a log message about `nonexistent_path` not existing, this is
 		// expected and clutters the test output.
-		err := flag.Set("log.level", "fatal")
+		log.AddFlags(kingpin.CommandLine)
+		_, err := kingpin.CommandLine.Parse([]string{"--log.level", "fatal"})
 		if err != nil {
 			t.Fatal(err)
 		}