* Introduce Agent-Test-Tool suite

* rename term

* Remove the local span and exit span register mechanism in Java agent scenario.

* Fix config, plugin, and document, as exit span is not required register anymore.

* Try to fix the test case expected data due to no register for exit span.

* Fix toolkit case.

* Remove exit span from plugin test framework document.

* Update protocol, FAQ, and CHANGELOG documents to highlight this change.

* Fix NPE when no entry span in the whole segment. Set endpoint to null in segment entity.

* Fix the snapshot and add inexistence operation name id.

* Fix several async cases.

* Fix undertow test case.

* Fix wrong error log name.

* Keep name consistent with 6.x concepts.

* Try to fix 3 async scenarios.

* Fix okhttp case.

* Fix Spring Async case.

* Fix another NPE

* Fix NPE when first span has no endpoint id when it is local or exit span.

* Still fill first operation name when no endpoint id.

* check agent register status

* update

* remove healtch-check segment

* update

* fix some expectedData.yml

* remove netty-socketio-scenario from Jenkinsfile

* fix

* immigrate spring async scenario

* fix rat

* Fix async not in effect

* immigrate spring scenario

* immigrate spring scenario

* fix

* immigrate spring scenario

* rollback

* fix log4j2.xml