add empty constructors for mocking

core/src/main/groovy/com/muwire/core/connection/ConnectionManager.groovy

@@ -10,6 +10,8 @@ abstract class ConnectionManager {
 
 	final EventBus eventBus
 	
+	ConnectionManager() {}
+	
 	ConnectionManager(EventBus eventBus) {
 		this.eventBus = eventBus
 	}

core/src/main/groovy/com/muwire/core/hostcache/HostCache.groovy

@@ -23,6 +23,8 @@ class HostCache extends Service {
 	final Destination myself
 	final Map<Destination, Host> hosts = new ConcurrentHashMap<>()
 	
+	HostCache(){}
+	
 	public HostCache(TrustService trustService, File storage, int interval, 
 		MuWireSettings settings, Destination myself) {
 		this.trustService = trustService