Stabilize ODS E2E tests and improve execution time by moving jenkins agents to a separated own project

Current Problem:
The ODS E2E tests are regularly impacted by broken builds of the jenkins agents dockerfiles (located in folder common).
This leads to permanent overhead of fixing the broken dockerfile.
The main problem is that the jenkins agent images are build from scratch (sequentially) during the setup of ODS E2E test environment (ODSBox).
This make the whole E2E tests strategy very unstable. Unstable E2E builds delay the merge of PRs.

Proposed Solution:
This request proposes to decouple the creation of the jenkins agent images from the build of ODS E2E tests environment.
To achieve this we would need to refactor out the folder common to its own repository. During the CI build of this new repository, the created docker images would be published to dockerhub. The published images would be imported during the tests execution.

This strategy is not new for OpenDevStack project. It is currently applied to create the docker image opendevstackorg/ods-jenkins-agent-base-centos7, which is build during the CI build of ods-core. Same strategy is used to release the provisioning app.

Benefits:
By doing this the ODS E2E tests would depend on published docker image, instead of images build from scratch.
This will not only stabilize the whole E2E tests process, also the execution time will reduced by aprox. 1,5 hrs.