Update all "incubator-skywalking" to "skywalking" ,"incubator-servicecomb-java-chassis" to "servicecomb-java-chassis" correctly, and ".gitmodules" will update at #2531 (#2548)

* Provide consul cluster plugin.

* Change log and application config file.

* Add consul's config item into the docker's application.yml.

* Fixed bug.

* Add consul description into  readme.

* Add okhttp component license.

* feat:Active System.env Config In Both Collector And agent.config.
1、moving related codes into apm-util module.
2、update Setting-override.md about how to use.

* resolve docs.

* typo

* finish test case.

* Update README.md

* support set config from system.envs.

* Buffer stream.

* Buffer file reader.

* Register start up.

* Service inventory register test success.

* Use annotation to instead of definition file.

* Cluster module implementation finished.