Cloudstack-2997 Make haproxy maxconn configurable

Signed-off-by: Abhinandan Prateek <aprateek@apache.org>

Conflicts:
	api/src/org/apache/cloudstack/api/ApiConstants.java
	engine/schema/src/com/cloud/offerings/NetworkOfferingVO.java
	server/src/com/cloud/network/router/VirtualNetworkApplianceManagerImpl.java
	setup/db/db/schema-410to420.sql