Fix NoClassDefFoundError when Mockito is missing

Update MockReset class to check for the presence of the MockUtil class
before attempting to use it.

Fixes gh-7065

spring-boot-samples/spring-boot-sample-test-nomockito/src/test/java/sample/testnomockito/SampleTestNoMockitoApplicationTest.java

@@ -0,0 +1,32 @@
+package sample.testnomockito;
+
+import org.junit.Test;
+import org.junit.runner.RunWith;
+
+import org.springframework.beans.factory.annotation.Autowired;
+import org.springframework.context.ApplicationContext;
+import org.springframework.test.context.junit4.SpringRunner;
+
+import static org.assertj.core.api.Assertions.assertThat;
+
+/**
+ * Tests that {code ResetMocksTestExecutionListener} and
+ * {@code MockitoTestExecutionListener} gracefully degrade when Mockito is not on the
+ * classpath.
+ *
+ * @author Madhura Bhave
+ */
+@RunWith(SpringRunner.class)
+public class SampleTestNoMockitoApplicationTest {
+
+	// gh-7065
+
+	@Autowired
+	private ApplicationContext context;
+
+	@Test
+	public void contextLoads() throws Exception {
+		assertThat(this.context).isNotNull();
+	}
+
+}