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.

// 
                isJvmRefer = InjvmProtocol.getInjvmProtocol().isInjvmRefer(tmpUrl);
            }
        } else {
            isJvmRefer = isInjvm();
        }
        return isJvmRefer;
    }
    protected boolean shouldCheck() {
        Boolean shouldCheck = isCheck();
        if (shouldCheck == null && getConsumer()!= null) {
            shouldCheck = getConsumer().isCheck();
        }
        if (shouldCheck == null) {
            // 
            shouldCheck = true;
        }
        return shouldCheck;
    }
    protected boolean shouldInit() {
        Boolean shouldInit = isInit();
        if (shouldInit == null && getConsumer() != null) {
            shouldInit = getConsumer().isInit();
        }
        if (shouldInit == null) {
            // 
            return false;
        }
        return shouldInit;
    }