User can request job logs be written to S3

[robert-clegg-tessella]

Sub-task to #16

User can call a writelogs handler with body {"job name": "example-job"}. The web app will get the logs for that job and write them to the kubernetes bucket in S3 at outputs/example-job/log.txt

Subsequent tickets will:

• generalise this process to all jobs that have completed
• improve the configuration
• call the method on a cron job

Acceptance criteria

• [x] A POST request to the new writelogs handler with body {"job_name": "{name of job}"}where the job exists produces a file in thekubernetesbucket in S3 atoutputs/example-job/log.txt`
• [x] The contents of the produced log file matches those obtained by running kubectl logs {spark job name}-driver from a command window (with kubectl access to the kubernetes cluster)
• [x] If the job does not exist a 404 is returned
• [x] If "job_name" argument is missing from the request a 400 is returned with a message stating it is a required property - Fail. Error message include unrelevant details "data": "'job_name' is a required property\n\nFailed validating 'required' in schema:\n {'properties': {'job_name': {'type': 'string'}},\n 'required': ['job_name'],\n 'type': 'object'}\n\nOn instance:\n {}"
• [x] The job is not deleted from the cluster after calling writelogs on it
• [x] Calling the handler a second time for the same job overwrites the log file previously produced

[robert-clegg-tessella]

@vidhyamanojkumar The 400 response is as expected: this is a standard response from the JSON schema validate method.