Set HAProxy timeout to 3h for Horizon HTTP

puppet-haproxy default timeout value of 1m is causing 504 Gateway Timeout
errors when uploading large images via Horizon Dashboard.

Change-Id: I07a666b17c20d39d4adcbcd1be69df42c2a1ddc2
Closes-Bug: #1326082
Merge "Set HAProxy timeout to 3h for Horizon HTTP" into stable/5.0