* 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.

* set up CI-IT action and Split Plugin-Tests

* update

* Immigrate tests okhttp scenario

* Fix Header.

* Fix license Header.

* Modify code follow the reivew suggestions.

* Fix expected.xml

* Restore the missed config

* Update okhttp elapsed time.

* Update total time for Group1.

* Fix the missed operationNames.

* [test/plugin] immigrate test hystrix scenario.

* change package name.

* add start script.

* plugin code

* NPE FIX

* [test/plugin] add elasticsearch 7.x plugin test scenario.

* refresh index, make can search.

* remove unused package.

* update supported framework document.

* fix service name repeat.

* Rabbitmq plugin e2e test migration

* 3753-code review fixes

* 3753-test-case-improvements

* Update pom.xml

Remove the repo addresses.

* Update Plugin-test.md

* immigrate test feign scenario.

* add license.

* update use test skeleton.

* delete repeat spring-boot starter dependence.

* add support-list version.

* Add elasticsearch 6.x plugin & elasticsearch 6.x test scenario

* jedis scenario

* update doc

* fix archetypes

* fix log4j

* provide archetypes for testcase

* merge undertow scenario

* update elapsed time

* Add SkyWalking plugin test framework doc

* Remove Chinese.

* Add a description to the env variable, CASE_SERVER_IMAGE_VERSION

* Fix typo

* Change paragraph structure.