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

@@ -0,0 +1,10 @@
+// +build appengine
+
+package logrus
+
+import "io"
+
+// IsTerminal returns true if stderr's file descriptor is a terminal.
+func IsTerminal(f io.Writer) bool {
+	return true
+}