Update traefik dependencies (docker/docker and related) (#1823)

Update traefik dependencies (docker/docker and related)

- Update dependencies
- Fix compilation problems
- Remove vdemeester/docker-events (in docker api now)
- Remove `integration/vendor`
- Use `testImport`
- update some deps.
- regenerate the lock from scratch (after a `glide cc`)

vendor/github.com/docker/distribution/context/util.go

@@ -0,0 +1,24 @@
+package context
+
+import (
+	"time"
+)
+
+// Since looks up key, which should be a time.Time, and returns the duration
+// since that time. If the key is not found, the value returned will be zero.
+// This is helpful when inferring metrics related to context execution times.
+func Since(ctx Context, key interface{}) time.Duration {
+	if startedAt, ok := ctx.Value(key).(time.Time); ok {
+		return time.Since(startedAt)
+	}
+	return 0
+}
+
+// GetStringValue returns a string value from the context. The empty string
+// will be returned if not found.
+func GetStringValue(ctx Context, key interface{}) (value string) {
+	if valuev, ok := ctx.Value(key).(string); ok {
+		value = valuev
+	}
+	return value
+}