Add deadline to break the connection. We use the default of 5 seconds.
After this the backend is marked unhealthy and not used for some time.
Fixes#467
* middleware/proxy
Use connection pooling for communicating with an upstream, instead of
opening a new socket every time.
This makes the proxy more efficient and allowed for some cleanups.
* Some cleanups
* Some fixes
* more
* Kill pool
* Add nil check
* remove pool
