Feature: Add Clean Up Handler to Executor

[williams-jack]

Feature/Problem Description

During the process of running a grading job on Orca, if a container is created but not started, then it will need to be cleaned up from the local Docker registry. To ensure this happens, a clean up handler is installed into the grading job executor, which the docker version of this class takes advantage of.

Solution (Changes Made)

• _cleanup_handler added on class GradingJobExecutor
  • DockerGradingJobExecutor implements this method and removes the container if it is found to exist. *InvalidWorkerStateException thrown if container exists and could not be cleaned up, as this means we may not be able to clean up resources successfully on the worker.

[blerner]

Shouldn't the tests be passing?

[williams-jack]

Shouldn't the tests be passing?

They will once we merge in the other PR (#79)