Sets a defaultInstance for WireMock server

without this change we're not resetting default instances upon test finish
with this change we're resetting the default intance and setting it once more upon configuration startup

fixes gh-1081

spring-cloud-contract-wiremock/src/main/java/org/springframework/cloud/contract/wiremock/WireMockConfiguration.java

@@ -119,6 +119,9 @@ public class WireMockConfiguration implements SmartLifecycle {
 		if (!this.beanFactory.containsBean(WIREMOCK_SERVER_BEAN_NAME)) {
 			this.beanFactory.registerSingleton(WIREMOCK_SERVER_BEAN_NAME, this.server);
 		}
+		if (isRunning()) {
+			updateCurrentServer();
+		}
 	}
 
 	private void logRegisteredMappings() {
@@ -130,6 +133,7 @@ public class WireMockConfiguration implements SmartLifecycle {
 
 	void resetMappings() {
 		this.server.resetAll();
+		WireMock.reset();
 		logRegisteredMappings();
 	}