Error handling in the `_process_job` funtion

[TheBits]

Many places in the "_process_job" function require error handling.

• [ ] RunnerClient.pull() inside the _process_running function can raise RequestException
• [ ] ShimClient.submit() inside the _process_provisioning_with_shimfunction can raiseRequestException`
• [ ] Inside the _process_pulling_with_shim funcation, ShimClient.pull() and RunnerClient.healthcheck() can raise ReqeustException
• [ ] Exceptions from RunnerClient.submit(), RunnerClient.upload() and RunnerClient.run_job() inside the _submit_job_to_runner function are not handled
• [ ] The _get_job_code can raise a botocore exception