CLOUDSTACK-7184: xenheartbeat gets passed timeout and interval
(cherry picked from commit 4d065b9a3a336d59902c266202c1094509c007d2)

Conflicts:
	plugins/hypervisors/xenserver/src/com/cloud/hypervisor/xenserver/discoverer/XcpServerDiscoverer.java
	plugins/hypervisors/xenserver/src/com/cloud/hypervisor/xenserver/resource/CitrixResourceBase.java
	server/src/com/cloud/configuration/Config.java
	server/src/com/cloud/configuration/ConfigurationManagerImpl.java
	server/src/com/cloud/resource/DiscovererBase.java