tests: deflake TestHTTP_NodeDrain
tests: deflake TestHTTP_NodeDrain

A node may be recognized as not running any allocs and have its drain
flag reset before the test queries it.

dvusboy/nomad,hashicorp/nomad,dvusboy/nomad,dvusboy/nomad,burdandrei/nomad,hashicorp/nomad,hashicorp/nomad,burdandrei/nomad,dvusboy/nomad,dvusboy/nomad,hashicorp/nomad,dvusboy/nomad,hashicorp/nomad,burdandrei/nomad,burdandrei/nomad,burdandrei/nomad,hashicorp/nomad,burdandrei/nomad,burdandrei/nomad,dvusboy/nomad