nms-10009: Use classBasedStrategy always when it can be instantiable
There are two instances of Snmp4JStrategy, one default and other from osgi service.
Second instance is replacing USM from SecurityModels.getInstance() which is causing users to be removed.
Although default and osgi should have different classes for SecurityModels.getInstance() sometimes they are same instance.
To solve this, we always instantiate classBasedStrategy on OpenNMS and don't register OSGI instance.
When classBasedStrategy is not instatiable (on Minion) we use instance from OSGI service registry.