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/Sirupsen/logrus/terminal_appengine.go

@@ -1,8 +0,0 @@
-// +build appengine
-
-package logrus
-
-// IsTerminal returns true if stderr's file descriptor is a terminal.
-func IsTerminal() bool {
-	return true
-}