Added getWriteLock() syncs to the class to synchronize writes to the config.
These missing locks were causing ConcurrentModificationExceptions inside
Collectd. Fixes bug NMS-6277.
Fixed bug NMS-6279 by adding synchronized() blocks around all access to List
fields inside ThresholdingSet.
Cleaned up EventUtils.toString() method.
Fixed stack trace in bug NMS-6280 by throwing FileNotFoundException when
the label of the resource cannot be calculated. Cleaned up label calculation
code inside CollectionResourceWrapper.
Merge branch '1.10' into 1.12

Conflicts:
	opennms-dao/src/main/java/org/opennms/netmgt/config/collector/ResourceIdentifier.java
	opennms-services/src/main/java/org/opennms/netmgt/collectd/IfInfo.java
	opennms-services/src/main/java/org/opennms/netmgt/collectd/PersistOperationBuilder.java
	opennms-services/src/main/java/org/opennms/netmgt/config/PollOutagesConfigManager.java
	opennms-services/src/main/java/org/opennms/netmgt/threshd/CollectionResourceWrapper.java
	opennms-services/src/main/java/org/opennms/netmgt/threshd/ThresholdingSet.java
	opennms-services/src/main/java/org/opennms/netmgt/threshd/ThresholdingVisitor.java