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