vendor: migrate to glide

cmd/vendor/github.com/prometheus/client_golang/prometheus/.gitignore

@@ -1 +0,0 @@
-command-line-arguments.test

cmd/vendor/github.com/prometheus/client_golang/prometheus/README.md

@@ -1,53 +0,0 @@
-# Overview
-This is the [Prometheus](http://www.prometheus.io) telemetric
-instrumentation client [Go](http://golang.org) client library.  It
-enable authors to define process-space metrics for their servers and
-expose them through a web service interface for extraction,
-aggregation, and a whole slew of other post processing techniques.
-
-# Installing
-    $ go get github.com/prometheus/client_golang/prometheus
-
-# Example
-```go
-package main
-
-import (
-	"net/http"
-
-	"github.com/prometheus/client_golang/prometheus"
-)
-
-var (
-	indexed = prometheus.NewCounter(prometheus.CounterOpts{
-		Namespace: "my_company",
-		Subsystem: "indexer",
-		Name:      "documents_indexed",
-		Help:      "The number of documents indexed.",
-	})
-	size = prometheus.NewGauge(prometheus.GaugeOpts{
-		Namespace: "my_company",
-		Subsystem: "storage",
-		Name:      "documents_total_size_bytes",
-		Help:      "The total size of all documents in the storage.",
-	})
-)
-
-func main() {
-	http.Handle("/metrics", prometheus.Handler())
-
-	indexed.Inc()
-	size.Set(5)
-
-	http.ListenAndServe(":8080", nil)
-}
-
-func init() {
-	prometheus.MustRegister(indexed)
-	prometheus.MustRegister(size)
-}
-```
-
-# Documentation
-
-[![GoDoc](https://godoc.org/github.com/prometheus/client_golang?status.png)](https://godoc.org/github.com/prometheus/client_golang)