Create .cortex dir if not present in Python Client

[RobertLucian]

If the ~/.cortex dir doesn't exist beforehand and a cluster-up/down is initiated using the python client installation (still using the binary), that will result in a FileNotFound error:

# example error from https://app.circleci.com/pipelines/github/cortexlabs/cortex/8642/workflows/e8042290-c5f1-4c8a-a278-aac2029056ec/jobs/11332
FileNotFoundError: [Errno 2] No such file or directory: '/home/circleci/.cortex/client-id.txt'

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checklist:

• run make test and make lint
• test manually (i.e. build/push all images, restart operator, and re-deploy APIs)