Harden http.Serve() with sensible Timeouts

#### Version information: master

#### Type: Enhancement

#### Priority: P4

#### Description:
Currently we do:

https://github.com/ipfs/go-ipfs/blob/67a1b3e1bfe9d05478f15068f31cc6868f12a74f/core/corehttp/corehttp.go#L83

But https://blog.gopheracademy.com/advent-2016/exposing-go-on-the-internet/ shows that it is better to initialize a Server object and set sensible timeouts:


Example:
```
srv := &http.Server{
ReadTimeout: 5 * time.Second,
WriteTimeout: 10 * time.Second,
IdleTimeout: 120 * time.Second,
Handler: serveMux,
}
```

(IdleTimeout is only in Go 1.8)