[CIT-442] Refactor system test cases (#565)

* Switch to snake case directory names for software-management-end-to-end

* Switch to snake case directory names

Procedure:
ls -1 | grep '-'
for i in * ; do git mv $i ${i//-/_} ; done
Ignore move into itself errors

* Move tests to tedge folder

* Move test to smoketest folder

* Move tests to analytics folder

* Move tests to cloud_c8y

* Move test to tedge_connect

* Move tests to local_mqtt

* Move tests to local_mqtt

* Move test to tedge_mapper_c8y

* Move test to tedge_mapper_c8y

* Move test to smoketests

* Move tests to tedge_connect

* Rename folder to plugin_apt

* Rename folder to plugin_docker

* Fix side effects of renaming

* Fix sideeffects of renaming

* Move device id and port change tests to misc_features

* Update readme

* Move pythonpath to pysysproject.xml