Handle redirects (HTTP/307)

[harmw]

The following can be observed on a regular Mesos cluster, when we try to launch vamp-gateway-agent:

2018/03/05 12:10:26.283428 run.go:124: WORKFLOW - HTTP REQUEST [0] {"protocol":"http:","port":"5050","hostname":"mesos-master.service.consul","method":"GET","headers":{},"path":"/master/slaves"}
2018/03/05 12:10:26.297016 run.go:124: WORKFLOW - HTTP RESPONSE [0] 307
2018/03/05 12:10:26.297665 run.go:122: ERROR -  WORKFLOW - events.js:160
2018/03/05 12:10:26.297687 run.go:122: ERROR -  WORKFLOW -       throw er; // Unhandled 'error' event
2018/03/05 12:10:26.297695 run.go:122: ERROR -  WORKFLOW -       ^
2018/03/05 12:10:26.297705 run.go:122: ERROR -  WORKFLOW - 
2018/03/05 12:10:26.297716 run.go:122: ERROR -  WORKFLOW - Error: [307]: 
2018/03/05 12:10:26.297736 run.go:122: ERROR -  WORKFLOW -     at IncomingMessage.response.on (/usr/local/vamp/node_modules/vamp-node-client/http.js:38:22)
2018/03/05 12:10:26.297743 run.go:122: ERROR -  WORKFLOW -     at emitNone (events.js:91:20)
2018/03/05 12:10:26.297760 run.go:122: ERROR -  WORKFLOW -     at IncomingMessage.emit (events.js:185:7)
2018/03/05 12:10:26.297767 run.go:122: ERROR -  WORKFLOW -     at endReadableNT (_stream_readable.js:974:12)
2018/03/05 12:10:26.297779 run.go:122: ERROR -  WORKFLOW -     at _combinedTickCallback (internal/process/next_tick.js:74:11)
2018/03/05 12:10:26.297786 run.go:122: ERROR -  WORKFLOW -     at process._tickCallback (internal/process/next_tick.js:98:9)

This happens because we are trying our request against any Mesos-master machine in the cluster. Mesos will happily acknowledge this request with a redirect to the current-cluster-leader. Vamp is just not wired to follow that, given that it only looks for answers in the range of HTTP/200-299.

Dumbing it down to just a simple curl:

/ # curl -I 10.204.104.49:5050/master/slaves
HTTP/1.1 307 Temporary Redirect
Date: Mon, 05 Mar 2018 12:16:18 GMT
Location: //mesos-master-i-0b08fddeaa8778de9.play.ground.dev.blaze.ps:5050/master/slaves
Content-Length: 0

Ideally, should this (specifically 307) be seen we should probably be following the Location header.