ref(probes): move k8s probe from liveness into readiness

[kmala]

Summary of Changes

add probe to check the status of the controller

Issue(s) that this PR Closes

Closes #181

Associated End To End Test PR(s)

Associated Documentation PR(s)

Associated Design Document(s)

Testing Instructions

Please provide a detailed list for how to test the changes in this PR.

1. Create a Deis Cluster
2. check the status of the builder and it should be serving
3. now stop the controller and check the status of the builder, it should still be up but not ready to serve requests

Pull Request Hygiene TODOs

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• Your pull request is concise and to the point (make another PR for refactoring nearby code)
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