Add httpclose option to default haproxy config

API DELETE calls were hanging as they return a 204. Without option
httpclose, these connections remain open and from a client's
perspective, the call returned no data. It sees this as a failure.
These failures have all kinds of rippling effects on things like
Horizon.
Merge pull request #405 from craigtracey/httpclose

Add httpclose option to default haproxy config