When I set `path` in ServiceConfig or `contextpath` in ProtocolConfig, RestProtocol throws NPE on this line:
https://github.com/apache/incubator-dubbo/blob/master/dubbo-rpc/dubbo-rpc-rest/src/main/java/org/apache/dubbo/rpc/protocol/rest/RestProtocol.java#L93
```java
Class implClass = ApplicationModel.getProviderModel(url.getServiceKey()).getServiceInstance().getClass();
```

<dubbo:service path="test" interface="org.apache.dubbo.samples.rest.api.facade.UserRestService" ref="userRestService"
                   protocol="rest" validation="true"/>

This is because we use `group/interface:version` as the key when putting ProviderModel:
```java
Application.initProviderModel(group/interface:version, providerModel)
```
but use `group/path:version` to get, as showed above.

I think to unify to `path` would solve this problem.

}
    @Test
    public void test_javaNetUrl() throws Exception {
        java.net.URL url = new java.net.URL("http://admin:hello1234@10.20.130.230:20880/context/path?version=1.0.0&application=morgan#anchor1");
        assertEquals("http", url.getProtocol());
        assertEquals("admin:hello1234", url.getUserInfo());
        assertEquals("10.20.130.230", url.getHost());
        assertEquals(20880, url.getPort());
        assertEquals("/context/path", url.getPath());
        assertEquals("version=1.0.0&application=morgan", url.getQuery());
        assertEquals("anchor1", url.getRef());
        assertEquals("admin:hello1234@10.20.130.230:20880", url.getAuthority());
        assertEquals("/context/path?version=1.0.0&application=morgan", url.getFile());
    }
    @Test
    public void test_Anyhost() throws Exception {
        URL url = URL.valueOf("dubbo://0.0.0.0:20880");
        assertEquals("0.0.0.0", url.getHost());
        assertTrue(url.isAnyHost());
    }
    @Test
    public void test_Localhost() throws Exception {
        URL url = URL.valueOf("dubbo://127.0.0.1:20880");
        assertEquals("127.0.0.1", url.getHost());
        assertTrue(url.isLocalHost());
        url = URL.valueOf("dubbo://127.0.1.1:20880");
        assertEquals("127.0.1.1", url.getHost());
        assertTrue(url.isLocalHost());
        url = URL.valueOf("dubbo://localhost:20880");
        assertEquals("localhost", url.getHost());