as7plugin: let MemoryPoolComponent start even if the underlying server is down

This is to avoid ugly exception logs like:

2014-03-05 09:55:17,436 ERROR [main] (rhq.core.pc.inventory.InventoryManager)- Exception thrown while activating [Resource[id=10397, uuid=353b527e-e9d3-4486-a04d-dbd5e2f735db, type={JBossAS7}Memory Pool Resource, key=core-service=platform-mbean,type=memory-pool,name=PS_Old_Gen, name=PS_Old_Gen, parent=memory-pool]].
org.rhq.core.clientapi.agent.PluginContainerException: Failed to start component for Resource[id=10397, uuid=353b527e-e9d3-4486-a04d-dbd5e2f735db, type={JBossAS7}Memory Pool Resource, key=core-service=platform-mbean,type=memory-pool,name=PS_Old_Gen, name=PS_Old_Gen, parent=memory-pool] - Failed to read attribute [usage-threshold-supported] of address [core-service=platform-mbean,type=memory-pool,name=PS_Old_Gen] - response: Result{outcome='failure', failureDescription=The server closed the connection before sending the response, rolled-back=false, rolledBack=false}
	at org.rhq.core.pc.inventory.InventoryManager.activateResource(InventoryManager.java:2070)
	at org.rhq.core.pc.inventory.InventoryManager.activateAndUpgradeResourceRecursively(InventoryManager.java:3590)
	at org.rhq.core.pc.inventory.InventoryManager.activateAndUpgradeResourceRecursively(InventoryManager.java:3592)
	at org.rhq.core.pc.inventory.InventoryManager.activateAndUpgradeResourceRecursively(InventoryManager.java:3592)
	at org.rhq.core.pc.inventory.InventoryManager.activateAndUpgradeResourceRecursively(InventoryManager.java:3592)
	at org.rhq.core.pc.inventory.InventoryManager.activateAndUpgradeResourceRecursively(InventoryManager.java:3592)
	at org.rhq.core.pc.inventory.InventoryManager.activateAndUpgradeResources(InventoryManager.java:3566)
	at org.rhq.core.pc.inventory.InventoryManager.initialize(InventoryManager.java:287)
	at org.rhq.core.pc.PluginContainer.initialize(PluginContainer.java:290)
	at org.rhq.enterprise.agent.AgentMain.startPluginContainer(AgentMain.java:1943)
	at org.rhq.enterprise.agent.AgentMain.start(AgentMain.java:697)
	at org.rhq.enterprise.agent.AgentMain.main(AgentMain.java:438)