Re-think integration vendoring

- remove docker/docker from  Traefik vendor (unused)
- use `ignore` for all Traefik vendor in integration glide.
- defined only integration specific version of the dependencies.

integration/vendor/github.com/opencontainers/runc/libcontainer/user/lookup.go

@@ -2,13 +2,15 @@ package user
 
 import (
 	"errors"
-	"fmt"
 	"syscall"
 )
 
 var (
 	// The current operating system does not provide the required data for user lookups.
 	ErrUnsupported = errors.New("user lookup: operating system does not provide passwd-formatted data")
+	// No matching entries found in file.
+	ErrNoPasswdEntries = errors.New("no matching entries in passwd file")
+	ErrNoGroupEntries  = errors.New("no matching entries in group file")
 )
 
 func lookupUser(filter func(u User) bool) (User, error) {
@@ -27,7 +29,7 @@ func lookupUser(filter func(u User) bool) (User, error) {
 
 	// No user entries found.
 	if len(users) == 0 {
-		return User{}, fmt.Errorf("no matching entries in passwd file")
+		return User{}, ErrNoPasswdEntries
 	}
 
 	// Assume the first entry is the "correct" one.
@@ -75,7 +77,7 @@ func lookupGroup(filter func(g Group) bool) (Group, error) {
 
 	// No user entries found.
 	if len(groups) == 0 {
-		return Group{}, fmt.Errorf("no matching entries in group file")
+		return Group{}, ErrNoGroupEntries
 	}
 
 	// Assume the first entry is the "correct" one.