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
CLOUDSTACK-7527 reboot faster by writing to /proc/sysrq-trigger

(cherry picked from commit d04f59a30d130dbb83f162af6e67334fe2c9cef0)
CLOUDSTACK-7184 retry-wait loop config to deal with network glitches

(cherry picked from commit a29f954a269c992307f0410df88ca4ac7a0b82a0)

Conflicts:
	engine/orchestration/src/com/cloud/agent/manager/DirectAgentAttache.java