fix ut stable, #2227 (#2302)

* fix ut, #2227

* add cache for travis ci

* fix travis problem, skip javadoc

Author: jerrick-zhu

.travis.yml

@@ -6,8 +6,15 @@ jdk:
     - oraclejdk8
     - openjdk7
 
+cache:
+  directories:
+  - '$HOME/.m2/repository'
+
+install:
+  - ./mvnw clean install -DskipTests=true -Dcheckstyle.skip=false -Drat.skip=false -Dmaven.javadoc.skip=true
+
 script:
-    - travis_wait 30 ./mvnw clean package
+    - travis_wait 30 ./mvnw test
 
 after_success:
   - bash <(curl -s https://codecov.io/bash)

dubbo-config/dubbo-config-api/src/test/java/com/alibaba/dubbo/config/RegistryConfigTest.java

@@ -69,6 +69,7 @@ public void testWait() throws Exception {
         registry.setWait(10);
         assertThat(registry.getWait(), is(10));
         assertThat(System.getProperty(Constants.SHUTDOWN_WAIT_KEY), equalTo("10"));
+        System.clearProperty(Constants.SHUTDOWN_WAIT_KEY);
     }
 
     @Test